Cortical interface for motor signal recording and sensory signal stimulation

ABSTRACT

The present invention consists of an implantable device with at least one package that houses electronics that sends and receives data or signals, and optionally power, from an external system through at least one coil attached to the at least one package and processes the data, including recordings of neural activity, and delivers electrical pulses to neural tissue through at least one array of multiple electrodes that is/are attached to the at least one package. The invention, or components thereof, is/are intended to be installed in the head, or on or in the cranium or on the dura, or on or in the brain. Variations of the embodiments depend on the physical locations of the coil(s), package(s) and array(s) with respect to the head, cranium, dura, and brain. Novel features of the present invention include the small size of the implantable package which houses the controller, the high number of electrodes that are provided for stimulation and/or sensing and stimulation, and the methods for manufacturing such a device. These features have unique applications in neural stimulation to treat or prevent disorders or disease.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/473,470, filed May 16, 2012, for Cortical Interface forMotor Signal Recording and Sensory Signal Stimulation, which is relatedto and incorporates by reference US Patent application 2009/0124965, forImplantable Device for the Brain, filed Jul. 25, 2008, now U.S. Pat. No.9,592,377.

FIELD OF THE INVENTION

The present invention is an implantable device for interfacing withneural tissue, primarily in order to record neural activity for thecontrol of a motor prosthesis. Secondarily the implantable devicestimulates neural tissue to provide sensory feedback.

BACKGROUND OF THE INVENTION

Neural tissue can be artificially recorded from and stimulated byprosthetic devices that sense or pass pulses of electrical currentthrough electrodes on such a device. The passage of current causeschanges in electrical potentials across neuronal membranes, which caninitiate neuron action potentials, which are the means of informationtransfer in the nervous system.

Based on this mechanism, it is possible to read information from, andinput information into, the central nervous system by coding or decodingthe sensory information as a sequence of electrical pulses, which arerelayed to the central nervous system via the prosthetic device. In thisway, it is possible to provide active motor prostheses and createartificial sensations.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

US Patent Application 2003/0109903 to Berrang describes a low profilesubcutaneous enclosure, in particular, and metal over ceramic hermeticpackage for implantation under the skin.

ECoG (electrocorticography) and LFP (local field potentials) have beenshown to provide data useful for BMIs (brain machine interfaces)(Mehring 2004) with LFPs containing more information content, but withhigher surgical risk. Also in 2004, an online study by Leuthardt et al.(Leuthardt 2004) showed that ECoG can support accurate BMI operationwith little user training. Additionally, this study also providedinitial evidence that ECoG signals contain information about thedirection of hand movements in particular. This finding was important inrevealing that high frequency gamma rhythms provide information notsimply on focal cortical activations, but rather convey specificinformation about cognitive intent. Distinct from single unit studies,this is one of the earliest demonstrations that cognitive intent couldbe inferred from large population scale cortical physiology.

EEG is non-invasive and has supported important BMI applications,including two- and three-dimensional movement control (Farwell 1988 a,b;Wolpaw 1991 a, b, 1994, 2002, 2004; Sutter 1992; McFarland 1993, 2008,2010; Pfurtscheller 1993; Birbaumer 1999; Kübler 1999, 2005;Pfurtscheller 2000; Milián 2004; Müller 2006; Vaughan 2006 Royer 2010).The highest functioning EEG-based BMIs, however, require a substantialdegree of user training and their performance is often not reliable.BMIs that are based on intracortical recordings of action potentialfiring rates or local field potentials are on the opposite end of theperformance and clinical spectrum (Georgopoulos 1986; Serruya 2002;Taylor 2002; Shenoy 2003; Anderson 2004; Lebedev 2005; Hochberg 2006;Santhanam 2006; Donoghue 2007; Velliste 2008). Though they can achieve ahigh level of multidimensional control, there still remains asignificant and unresolved question regarding the long-term functionalstability of intracortical electrodes, particularly for recording actionpotentials (Shain 2003; Donoghue 2004; Davids 2006). This lack of signaldurability has important clinical implications, because signal losswould require frequent replacement of the implant which would beneurosurgically unacceptable. Despite encouraging evidence that currentnon-invasive and invasive BMI technologies can actually be useful toseverely disabled individuals (Kübler 2005; Hochberg 2006; Sellers2010), these shortcomings and uncertainties remain substantial barriersto widespread clinical adoption and implementation in humans.

Compared to EEG, ECoG has major advantages: higher spatial resolution(e.g., 1.25 mm (subdural recordings (Freeman 2000; Leuthardt 2009)) and1.4 mm (epidural recordings (Slutzky 2010)) vs. several centimeters forEEG); higher amplitude (e.g., 50-100 μV maximum vs. 10-20 μV maximum forEEG); far less vulnerability to artifacts such as electromyographic(EMG) or electroocular (EOG) activity ((Freeman 2003) or (Ball 2009),respectively); and broader bandwidth (i.e., 0-500 Hz (Staba 2002) vs.0-40 Hz for EEG). With respect to the larger bandwidth of ECoG comparedto EEG, it is important to note that this advantage may be directlyrelated to the larger amplitude of ECoG. Because ECoG generally followsa 1/frequency drop-off in signal power (Miller 2009), task-related brainsignals may remain larger than the noise floor of theamplifier/digitizer, and thus be detectable, at higher frequencies thanfor EEG. Additionally, these higher gamma frequencies (60-500 Hz) havebeen shown to carry substantive information on cognitive motor andlanguage intentions, and provide vital information for cognitive controlfeatures that are poorly accessible with EEG. In addition to theseadvantages of signal and information quality, ECoG electrodes (which donot penetrate cortex) should provide greater long-term functionalstability (Pilcher 1973; Loeb 1977; Bullara 1979; Yuen 1987; Margalit2003) than intracortical electrodes, which induce complex histologicalresponses that may impair neuronal recordings. A recent study by Chao(2010) showed that the signal-to-noise ratio of ECoG signals, and thecortical representations of arm and joint movements that can beidentified with ECoG are stable over several months (Schalk 2010).

A fully integrated implantable architecture that combines electrodearray, signal amplification, and telemetry has many advantages increating a practical neural interface for a BMI based prosthetic limbsystem. Several such systems have been designed (Wise 2005; Harrison2007; Rouse 2011). Among them the 100-electrode wireless cortical neuralrecording system based on the Utah array (Harrison 2007) represents themost up-to-date state-of-the-art in terms of electrode count, systemintegration and telemetry. It contains an array of 100 amplifiers (60 dBgain), a 10 bit ADC (analog to digital converter), an inductive powerlink, 20 kbps forward telemetry data, and an FSK back telemetry linkwith a data rate of 345 kbps. However, this system is built to recordfrom a spike electrode array that has shown problems of long termencapsulation and signal degradation due in part to a mechanicalstiffness mismatch. Additionally, the implant does not have a hermeticpackage with proven long-term reliability, like the Argus II. The newestimplantable system intended for chronic BMI is the 16 electrode systembuilt from the Medtronic ActivaPC neural stimulator by adding a “brainactivity sensing interface IC” (Rouse 2011). By using ActivaPC's systemscheme, the main device is to be implanted in a place on the body awayfrom the head, and the sensing electrode array to be connected to thedevice through an extension connector and subcutaneous cable. The neuralsensing interface includes sub-μV resolution and is intended for bothLFP and ECoG based control. However, it is a prototype system that isbuilt for proof of concept and not a clinical device. Furthermore, theuse of the extension connector and long subcutaneous cable is stillsusceptible to infection and cannot avoid the relatively common leadbreakage problems associated with the ActivaPC device (Hamani 2006;Blomstedt 2005; Fernandez 2010). Additionally, having the amplifiers sodistant from the recording sites increases the introduction of noise.Also, the use of an implant battery limits its long term capabilities.Further, the long-leads limit MRI to low levels—an important clinicalconsideration.

No single state-of-the-art system contains all the key featuresnecessary for a practical, chronically implantable, and reliableCNS-interface system with a long life.

SUMMARY OF THE INVENTION

The present invention consists of an implantable device with at leastone package that houses electronics that send and receive data orsignals, and optionally, power, from an external system through at leastone coil attached to at least one package, and processes the data,including recordings of neural activity, and/or delivers electricalpulses to neural tissue through at least one array of multipleelectrodes that is/are attached to the at least one package. The deviceis adapted to electrocorticographic (ECoG) and local field potential(LFP) signals. The output signals provide control for a motor prosthesisand the input signals provide sensory feedback for the motor prosthesis.The invention, or components thereof, is/are intended to be installed inthe head, or on or in the cranium or on the dura, or on or in the brain.Variations of the embodiments depend on the physical locations of thecoil(s), package(s) and array(s) with respect to the head, cranium,dura, and brain. Novel features of the present invention include thesmall size of the implantable package which houses the controller, thehigh number of electrodes that are provided for sensing and/orstimulation, and the methods for manufacturing such a device. Thesefeatures have unique applications in neural sensing and/or stimulationto treat or prevent disorders or disease. Other novel features will bemade evident in the descriptions below.

The present invention includes an improved hermetic package connected toa thin film array and a coil, for implantation in the human body, andparticularly in the human head, for the purposes of sensing andstimulating the brain on the surface or at some depth. The implantabledevice of the present invention includes an electrically non-conductivesubstrate including electrically conductive vias through the substrate.A circuit is flip-chip bonded to a subset of the vias or tracesconnected to the vias. A second circuit is wire bonded to another subsetof the vias or traces connected to the vias. A cover is bonded to thesubstrate such that the cover, substrate, and vias form a hermeticpackage. Finally, at least one thin film electrode array is attached tothis package mechanically and electrically such that the electrode maysense neural activity or stimuli emitted from the electronics within thepackage, which then may be transmitted to areas of the brain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the preferred package for the present inventionillustrating basic structure and means of attachment.

FIG. 2A shows the preferred invention as implanted for neural recording.

FIG. 2B shows an alternate implantation location for brain surfacestimulation.

FIG. 3 is a perspective view of a partially built package showing thesubstrate, chip, and the package wall.

FIG. 4 is a perspective view of the hybrid stack placed on top of thechip.

FIG. 5 is a perspective view of the partially built package showing thehybrid stack placed inside.

FIG. 6 is a perspective view of the lid to be welded to the top of thepackage.

FIG. 7 is a view of the completed package attached to an electrodearray.

FIG. 8 is a cross-section of the package.

FIG. 9 is a top view of the ceramic substrate showing the metal tracesfor redirecting electrical connections.

FIG. 10A is a bottom view of the ceramic substrate showing the metaltraces for redirecting electrical connections.

FIG. 10B is a bottom view of the ceramic substrate prior tometallization showing the vias through the substrate.

FIG. 11 depicts a top view of a finished feedthrough assembly inaccordance with the present disclosure, comprised of a ceramic sheethaving electrically conductive vias extending therethrough.

FIG. 12 depicts a sectional view taken substantially along the plane12-12 of FIG. 11 showing the electrically conductive vias end flush withthe surfaces of the ceramic sheet.

FIG. 13 depicts a flow diagram illustrating a possible series of processsteps for fabricating a feedthrough assembly in accordance with thepresent disclosure.

FIGS. 14A-14M respectively depict the fabrication stages of afeedthrough assembly in accordance with the process flow illustrated inFIG. 13, wherein FIG. 14A depicts a sectional view of a ceramic sheet,and FIGS. 14B-C depict via holes being punched in the sheet of FIG. 14A.

FIGS. 14D-E depict exemplary stencil printing with vacuum pull downprocess.

FIG. 14F depicts paste inserted into the via holes.

FIGS. 14G-H depict exemplary multilayer lamination process.

FIG. 4I shows an exemplary laminated substrate.

FIGS. 14J-K depict lapping/grinding process.

FIGS. 14L-M depict dicing of the substrate to form multiple feedthroughassemblies.

FIG. 15 is the preferred implantation of the preferred invention in thebrain.

FIGS. 16A-E show the method of attaching a thin film array to theelectronics package.

FIGS. 17A-B show the thin film array of the present invention.

FIGS. 18A-C show the thin film array of the present invention in moredetail, and an implantation tool.

FIGS. 19A-B show the implantation location of the present invention.

FIGS. 20A-C show alternate implantation locations for the presentinvention.

FIGS. 21A-D show alternate embodiments including multiple implantablepackages.

FIGS. 22A-F show further alternate embodiments and configurations.

FIGS. 23A-C show further alternate embodiments, including a penetratingelectrode array.

FIG. 24 is a schematic diagram of the brain to further illustrate areaswhich could be stimulated by the present invention.

FIGS. 25A-25E depict molds for forming the flexible circuit array in acurve.

FIG. 26 depicts an alternate view of the invention with ribs to helpmaintain curvature and prevent tissue damage.

FIG. 27 depicts an alternate view of the invention with ribs to helpmaintain curvature and prevent tissue damage, fold of the flexiblecircuit cable, and a fold A between the circuit electrode array and theflexible circuit cable.

FIG. 28 depicts the flexible circuit array before it is folded andattached to the implanted portion.

FIG. 29 depicts the flexible circuit array, folded.

FIG. 30 depicts a flexible circuit array with a protective skirt.

FIG. 31 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array.

FIG. 32 depicts a flexible circuit array with a protective skirt bondedto the front side of the flexible circuit array.

FIG. 33 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array and molded around theedges of the flexible circuit array.

FIG. 34 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array, molded around the edgesof the flexible circuit array, and flush with the front side of thearray.

FIG. 35 is an enlarged view of a single electrode within the flexiblecircuit electrode array.

FIG. 36 depicts the flexible circuit array before it is folded andattached to the implanted portion, containing an additional fold betweenthe flexible electrode array and the flexible cable.

FIG. 37 depicts the flexible circuit array of FIG. 16, folded,containing an additional fold between the flexible electrode array andthe flexible cable.

FIG. 38 depicts a flexible circuit array of FIG. 17 with a protectiveskirt, and containing an additional fold between the flexible electrodearray and the flexible cable.

FIG. 39 depicts a top view of a flexible circuit array and flexiblecircuit cable showing an additional horizontal angle between theflexible electrode array and the flexible cable.

FIG. 40 depicts another variation without the horizontal angle betweenthe flexible electrode array and the flexible cable, but with anorientation of the electrodes in the flexible electrode array, as shownfor the variation in FIG. 19.

FIG. 41 depicts a top view of a flexible circuit array and flexiblecircuit cable wherein the array contains a slit along the length axis.

FIG. 42 depicts a top view of a flexible circuit array and flexiblecircuit cable wherein the array contains a slit along the length axiswith two attachment points.

FIG. 43 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array with a progressivelydecreasing radius.

FIG. 44 depicts a flexible circuit array with a protective skirt bondedto the front side of the flexible circuit array with a progressivelydecreasing radius.

FIG. 45 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array, and molded around theedges of the flexible circuit array with a progressively decreasingradius.

FIG. 46 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array, molded around the edgesof the flexible circuit array, and flush with the front side of thearray with a progressively decreasing radius.

FIG. 47 depicts a side view of the flexible circuit array with a skirtcontaining a grooved and rippled pad instead of a suture tab.

FIG. 48 depicts a side view of the enlarged portion of the skirt shownin FIG. 47 containing a grooved and rippled pad and a mattress suture.

FIG. 49 depicts a flexible circuit array with a protective skirt bondedto the front side of the flexible circuit array with individualelectrode windows.

FIG. 50 depicts a flexible circuit array with a protective skirt bondedto the back side of the flexible circuit array and molded around theedges of the flexible circuit array with individual electrode windows.

FIGS. 51-56 show several surfaces to be applied on top of the cable.

FIG. 57 depicts the top view of the flexible circuit array beingenveloped within an insulating material.

FIG. 58 depicts a cross-sectional view of the flexible circuit arraybeing enveloped within an insulating material.

FIG. 59 depicts a cross-sectional view of the flexible circuit arraybeing enveloped within an insulating material with open electrodes andthe material between the electrodes.

FIG. 60 depicts a cross-sectional view of the flexible circuit arraybeing enveloped within an insulating material with open electrodes.

FIG. 61 depicts a cross-sectional view of the flexible circuit arraybeing enveloped within an insulating material with electrodes on thesurface of the material.

FIG. 62 depicts a side view of the enlarged portion of the flexiblecircuit array being enveloped within an insulating material withelectrodes on the surface of the material inside the eye.

FIG. 63 shows the whole flexible polymer array with the bond pad and thetraces with holes at the edge of the electrode array.

FIG. 64 shows an enlarged view of the electrode array with holes at theedge for providing a protective skirt.

FIG. 65 shows a cross-sectional view of a polyimide array coated withPDMS (polydimethylsiloxane).

FIG. 66 shows a sequence of steps 1 to 8 for coating a polyimideelectrode with PDMS.

FIG. 67 shows a sequence of steps 1 to 7 for coating a polyimideelectrode with PDMS.

FIGS. 68A-D show a thin film array with penetrating electrodes.

FIGS. 69A-D show a thin film array with electrodes on both sides of thearray.

FIGS. 70A-C show penetrating electrodes individually mounted to a thinfilm array and insulated penetrating electrodes with openings on theirsides.

FIG. 71 shows an alternative penetrating flexible circuit electrodearray.

FIG. 72 shows a hybrid surface and penetrating flexible circuitelectrode array.

FIG. 73 shows an insertion tool for a penetrating flexible circuitelectrode array.

FIG. 74 is a block diagram of a motor control prosthesis using the brainimplant of the present invention.

In the following description, like reference numbers are used toidentify like elements. Furthermore, the drawings are intended toillustrate major features of exemplary embodiments in a diagrammaticmanner. The drawings are not intended to depict every feature of everyimplementation, nor relative dimensions of the depicted elements, andare not drawn to scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

This application is a cortically driven motor prosthesis: electrodesimplanted on or in a motor strip, which when activated cause involuntarymovements in the subject. The implant provides control for an externalrobotic prosthesis—an implant with recording electrodes on or in apre-motor (forward of motor strip) or motor strip, which sends datawirelessly to an external processor, which drives a robotic limb (arm,hand, leg, foot), or stimulates muscles in a deinervated arm, hand, leg,foot, face, tongue, etc.

A motor signal neural recorder and a somatosensory prosthesis providingmotor control and external or implantable sensors that respond to

-   -   1. Pressure    -   2. Temperature (heat or cold) or    -   3. Harmful stimuli such as sharp objects which send data to a        processor that then sends the information to an implanted        prosthesis with stimulating electrodes on or in the        somatosensory strip. In the preferred embodiment, the        implantable portion measures ECoG and LFP signals.

The preferred device provides for selectable sensing electrodes. Thatis, any electrode, or electrodes, within the array may be connected toany recording channel or any stimulation driver to adapt the device formost effective recording of neural activity. All programmable functionsare controlled by an external device through a bidirectional wirelesslink.

Several novel features of this system are described herein; small size(i.e. can be implanted on the brain or dura to eliminate cable tetheringeffects), novel stable high surface area electrode material, RF powered(i.e. no battery to replace), MRI compatibility, demonstratedbiostability in delicate neural tissue, paper-thin micro-machined arraycable designed to cross the sclera or dura interface without infectionrisk, 60 200 um disc electrodes in 3×5 mm area.

This invention includes recording capability to the stimulator with amodified mechanical configuration to permit epidural, subduralmicro-ECoG (electrocorticography), and/or intracortical LFP (local fieldpotential) signal recordings. Many approaches have been taken to BMIs(Brain Machine Interfaces). They range from non-invasive (butimpractical for portable use) MEG, PET, and fMRI, to very invasivemicroelectrode wires or arrays for recording single-unit actionpotentials.

Brain tissue has an elastic modulus in the range of 10-100 kPa. Many ofthe probes used, on the other hand, have elastic moduli on the order of160 GPa—a clear mismatch. The Argus II array, as described in U.S. Pat.No. 8,014,827 for Flexible Circuit Electrode Array, is polymerencapsulated with an elastic modulus of 2 MPa—much closer to the nativebrain tissue. This micro-machined array was designed to interface withthe retina of a moving eye (neural tissue with the consistency of 1-plywet tissue paper)—an even greater interface challenge than thecomparatively tougher brain tissue.

With modifications to the existing Argus II array design, it can beconfigured to be placed as a subdural micro-ECoG array, orintracortically as an LFP recording array. For micro-ECoG, the electrodearray would be similar to the current retinal prosthesis array, exceptit would be flat instead of curved making it easier to fabricate thanthe retinal array. One advantage of micro-machined arrays is that theelectrode size and spacing can be almost arbitrarily specified. We haveproduced arrays with electrodes as small as 25 μm in diameter up to aslarge as several millimeters. The array has a flexible thin-film cableto connect it to the electronics package (see FIG. 1).

To implant the Argus Il intracortically, the array is divided up into‘fingers’ to allow for penetration into the cortex with minimal trauma.The electrode size would be minimized to permit the fingers of the arrayto be as narrow as possible. Each finger would have multiple electrodesthat could be elongated to maximize electrode area while minimizingfinger width. Each finger would have a reinforced hole at the end of itto receive the tips of the insertion tool (introducer) which would beused to insert the electrodes through an incision.

Finally, a combined approach is envisioned with both subdural micro-ECoGelectrodes and intracortical electrodes. This approach is a hybrid ofthe two possible alternate embodiments.

Several new technologies were required to build the Argus II implant.Major technological advances were made in the array, electrode material,hermetic implantable package, and implantable interconnect. Theseadvances are discussed further below:

Thin-film electrode array (TFEA) is a thin film array (about 10 umthick) that employs a biocompatible polyimide as the substrate, withphotolithographically patterned platinum metallization. Severalmodifications were made to the TFEA manufacturing process in order toimprove metal to polyimide and polyimide to polyimide adhesion, andhence extend the lifetime of the device to many decades.

Accelerated soak testing of a dozen samples of the final design at 87°C. and, under 5 V DC bias, has resulted in a mean lifetime of 80 yearsand longest running samples have lifetimes in excess of 100 years.Flexural testing (120 degree bend around a 5 mm radius of curvature) oneight samples showed that each surpassed 25 million cycles withoutfailure.

Analytical testing of long-term implants after 14-months in a humansubject by SEM/EDX (Scanning electron microscope with energy dispersiveX-ray spectroscopy) confirms no change in array's polymer chemicalcomposition and no fibrosis encapsulation is evident.

Advanced Electrode Material: A novel electrode material, Platinum Gray'as described in U.S. Pat. No. 6,974,533 for Platinum Electrode andMethod of Manufacturing the Same, provides significantly lower impedancethan any other commercial material. This reduced impedance is importantfor recording microelectrodes since it improves the signal to noiseratio and reduces cross-talk (Rouse 2011).

Advanced Implantable Electronics Packaging: No polymer electronicscasing that we tested lasted more than a few months in soak tests. The‘hard case’ package of the Argus II described in U.S. patent applicationSer. No. 11/385,314, filed Mar. 20, 2006, for Package for an ImplantableNeural Stimulation Device, consists of a base ceramic layer withhermetic platinum feedthroughs and a solid metal side wall that isbrazed onto the ceramic. A lid, which also acts as the electrical returnfor the implant, is then welded onto the braze wall to complete thepackage. A high density implantable interconnect process to connect thepackage to the TFEA is also describe herein.

Final device testing: A dozen Argus II devices have undergone real timeand accelerated soak testing in the finished device level as part of avalidation protocol. To date, none of these devices have failed (leak ormaterial dissolution) and their lifetime is approaching 30 years. Inaddition, more than a dozen active Argus II devices have undergone invivo testing in canines for six months without a failure. The Argus IIimplant is the only device of its kind to pass the FDA's tough standardsfor long-term human trials. To date, Argus II has been implanted in 30patients worldwide. The longest implanted patients are approaching 4years of use, and no device failures have been observed except for oneintermittent RF link attributed to the misuse of a sharp surgical toolearly in the trial. The Argus II Neural Stimulator meets all thebiocompatibility requirements of ISO 10993-1 and FDA guidance G95-1. Theimplants were tested for cytotoxicity, irritation, sensitization, acutesystemic toxicity, pyrogenicity, subchronic toxicity, genotoxicity andimplantation.

Leveraging experience from successfully designing the chronicallyimplantable Argus II Retinal Prosthesis, the present invention implantsimilarly includes a coil, thin film electrode array, and implantelectronics housed in a hermetic package. For the present invention, theimplant coil is located subcutaneously under the scalp, or possibly onthe brain or dura, and receives power from an external coil placed overthe scalp through inductive coupling.

The implant power recovery circuit retrieves DC power from the RF powercarrier to supply the ASIC (Application Specific Integrated Circuit).Amplitude modulated data from the AES (Argus external system) is sent tothe implant at a data rate of 122 kbps. The transceiver on the ASIC chipdecodes this telemetry data (referred to as forward telemetry), whichcarries implant control commands that include electrode selection foreach neural sensing channel, gain selection, sampling control, and othersafety and diagnostic commands. The forward telemetry also supports CNS(Central nervous system) electrode stimulation commands for up to 60electrodes, which may be used in future designs of the system. The ArgusII implant ASIC is modified to include 16 neural sensing channels andreliably conveys this information to the AES. The channels each containa differential neural amplifier that can sense sub-μV neural signals anda band pass filter for a specified y band of 75-105 Hz, which can beassigned or reassigned to other frequencies by the AES. The amplifiedand band filtered signals from the specified channels are sampled by anADC without data reduction at a rate up to 480 Hz per channel and withsub-μV input resolution. Raw data from the ADC is streamed to the AESdirectly through a wireless link (referred to as back telemetry)designed with a bandwidth capable of handling the data flow in realtime. The back telemetry data words include a header and CRC (cyclicredundancy check) to ensure bit error detection. The back telemetryemploys a Frequency-shift Keying scheme whose carrier frequency isselected to minimize susceptibility to anticipated interfering signals.The ASIC also includes a dedicated channel and a 1 KHz test signalgenerator for analyzing electrode impedance values and thus determiningthe health of the electrode array.

The AES Subsystem

The AES is a modified version of the Argus II External System, designedto interface with the implant. The AES consists of telemetry electronicsand an embedded microprocessor system. The telemetry electronicsreceives and demodulates the back telemetry data, while simultaneouslyproviding power and forward telemetry to the implant. Data to theimplant is amplitude modulated at a modulation depth of 10% on the 3.156MHz power carrier. The microprocessor system uses a Texas InstrumentsOMAP 3530 microprocessor, which combines a 720 MHz ARM Cortex-A8 and a520 MHz DSP. This system monitors the health and safety of the implantwhile continuously streaming neural sensing commands to the implant andreceiving sensed neural data from the implant. In addition, the AES isresponsible for processing the sensed neural data in real time toextract spectral power, track power fluctuations and further analyze andformat the data to output multiple independent motor-control signals forthe interface module. Data flow to the interface module is managed inreal time, implementing error detection and correction schemes to ensurea high quality data link. The system also has the ability to store thehistory of chronic sensed neural data for offline analysis gearedtowards signal optimization and patient personalization. To enhance theoverall flexibility of the system, the AES firmware isfield-upgradeable.

The implant sub-component of the present invention is designed to be acompletely implantable neural sensing interface (for micro ECoG andLocal Field Potentials). The implant has integrated low-noise neuralsensing circuits and data telemetry close to the recording sites and isbased on a predictable device that has been clinically proven todemonstrate long-term hermeticity and device reliability. Extensivein-vitro and in-vivo verification and validation testing was performedprior to a 30 subject clinical trial with nearly 80 subject yearswithout a device failure (note: one intermittent device was traced to asurgical error). The small form factor of the implant facilitates aminimally invasive surgical procedure and has no end-of-life batteryrestrictions because no battery is required in the implant. The implanthas no need for transcutaneuous or subcutaneous wire leads which resultsin a low likelihood of complications such as infection, migration andmechanical damage to the leads. The implant is fully MRI compatible. TheAES subsystem is field programmable to configure sensing parameters andpower extraction algorithms and is built upon proven technologyoptimized for low power devices.

Overall, the present invention has the capability to robustly andreliably acquire and process neural signals (micro ECoG and Local FieldPotentials) in real time, generating output motor control signals thatare used to obtain up to 8 degrees of control for an arm prosthesis.

A preferred embodiment of the present invention, shown in FIG. 1,consists of an electronics package 14 that is preferably oval orcircular in shape (but other shapes are possible) less than 20 mm indiameter (preferably less than 15 mm and more preferably less than 11 mmin diameter), and that is less than 5 mm in height (preferably less than4 mm and more preferably less than 3.5 mm in height), that is mounted ontop of the cranium but under the skin. The package may include a featurefor mounting to the cranium such as a low profile flange 2 definingholes 3 to accommodate screws (not shown), or tabs 4 that allow screws,sutures, or staples to be taken to fix the package. Attached to, andproceeding from, the package 14 is a thin film lead 10 to be routed tothe tissue to be stimulated or recorded from.

FIG. 2 shows attachment of the package 14 to the cranium 7. Alternately,the package 14 may be affixed to the cranium through the use of one ormore straps, or the package 14 may be glued to the cranium using areversible or non-reversible adhesive attach. In this embodiment, thepackage, which protrudes from the cranium, is low profile and shaped ina manner that permits the scalp 8 to rest on top of the package withlittle or no irritation of the scalp. Additionally, edges of the packageare preferably rounded, and/or the package 14 may be encased in a softpolymer mold such as silicone to further reduce irritation. In otherembodiments, the package 14 may be attached to the scalp 8, brain 11, ordura 12. In embodiments with more than one package, each package may beattached to any of the scalp, cranium, dura, or brain.

The improved package of the present invention allows for miniaturizationof the package, which is particularly useful in brain sensors,stimulators, and other prostheses for electrical sensing and stimulationof neural tissue.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably, the secondary inductive coil 16 is madefrom wound wire. Alternately, the secondary inductive coil 16 may bemade from a flexible circuit polymer sandwich with wire traces depositedbetween layers of flexible circuit polymer. The electronics package 14and secondary inductive coil 16 are held together by the molded body 18.The molded body 18 holds the electronics package 14 and secondaryinductive coil 16 end to end. This is beneficial as it reduces theheight the entire device rises above the sclera. The design of theelectronics package (described below), along with a molded body 18 whichholds the secondary inductive coil 16 and electronics package 14 in theend to end orientation, minimizes the thickness or height above thesclera of the entire device.

The molded body 18 may also include the flange 2 or suture tabs 4. Themolded body 18, flange 2, and suture tabs 4 are preferably an integratedunit made of silicone elastomer. Silicone elastomer can be formed in apre-curved shape to match the curvature of the implantation site.However, silicone remains flexible enough to accommodate implantationand to adapt to variations in the curvature at a particular site.Alternately, the flange 2 and/or suture tabs 4 may be formed of the samematerial(s) as the package (that is, integrated with the package), andthe molded body 18 can be used to hold the coil 16 and package 18together.

Referring to FIG. 3, the hermetic electronics package 14 is composed ofa ceramic substrate 60 brazed to a metal case wall 62 which is enclosedby a laser welded metal lid 84. The metal of the wall 62 and metal lid84 may be any biocompatible metal such as Titanium, niobium, platinum,iridium, palladium, or combinations of such metals. The ceramicsubstrate is preferably alumina but may include other ceramics such aszirconia. The ceramic substrate 60 includes vias (not shown) made frombiocompatible metal and a ceramic binder using thick-film techniques.The biocompatible metal and ceramic binder is preferably platinum flakesin a ceramic paste, or frit, which is the ceramic used to make thesubstrate. After the vias have been filled, the substrate 60 is firedand lapped to thickness. The firing process causes the ceramic tovitrify binding the ceramic of the substrate with the ceramic of thepaste forming a hermetic bond.

The package wall 62 is brazed to the ceramic substrate 60 in a vacuumfurnace using a biocompatible braze material in the braze joint.Preferably, the braze material is a nickel titanium alloy. The brazetemperature is approximately 1000° Celsius. Therefore the vias and thinfilm metallization 66 must be selected to withstand this temperature.Also, the electronics must be installed after brazing. The chip 64 isinstalled inside the package using thermo-compression flip-chiptechnology. The chip is underfilled with epoxy to avoid connectionfailures due to thermal mismatch or vibration.

Referring to FIGS. 4 and 5, off-chip electrical components 70, which mayinclude capacitors, diodes, resistors, or inductors (passives), areinstalled on a stack substrate 72 attached to the back of the chip 64,and connections between the stack substrate 72 and ceramic substrate 60are made using gold wire bonds 82. Alternately, discrete components, ora circuit board, may be attached to the ceramic substrate. A flip-chipintegrated circuit and/or hybrid stack is preferred as it minimizes thesize of the package 14. The stack substrate 72 is attached to the chip64 with non-conductive epoxy, and the passives 70 are attached to thestack substrate 72 with conductive epoxy. Thin-film metallization 66 isapplied to both the inside and outside surfaces of the ceramic substrate60 and an ASIC integrated circuit chip 64 is bonded to the thin filmmetallization on the inside of the ceramic substrate 60.

Referring to FIG. 6, the electronics package 14 is enclosed by a metallid 84 that, after a vacuum bake-out to remove volatiles and moisture,is attached using laser welding. A getter (moisture absorbent material)may be added after vacuum bake-out and before laser welding of the metallid 84. Further, the metal lid 84 has a metal lip 86 to protectcomponents from the welding process and further insure a good hermeticseal. The entire package is hermetically encased. Hermeticity of thevias, braze, and the entire package is verified throughout themanufacturing process.

The implant secondary inductive coil 16, which provides a means ofestablishing the inductive link between the external processor (notshown) and the implanted device, preferably consists of gold wire. Thewire is insulated with a layer of silicone. The secondary inductive coil16 may be oval shaped. The conductive wires are wound in defined pitchesand curvature shape to satisfy both the functional electricalrequirements and the surgical constraints. The secondary inductive coil16, together with the tuning capacitors in the chip 64, form a parallelresonant tank that is tuned at the carrier frequency to receive bothpower and data.

Referring to FIG. 7, the flexible circuit thin film lead 10 includesplatinum conductors 94 insulated from each other and the externalenvironment by a biocompatible dielectric polymer 96, preferablypolyimide. One end of the array contains exposed electrode sites thatare placed in close proximity to the surface to be stimulated orrecorded from 333. The other end contains bond pads 92 that permitelectrical connection to the electronics package 14. The electronicspackage 14 is attached to the flexible circuit 10 using a flip-chipbumping process, and is epoxy underfilled. In the flip-chip bumpingprocess, bumps containing conductive adhesive placed on bond pads 92 andbumps containing conductive adhesive placed on the electronics package14 are aligned and cured to build a conductive connection between thebond pads 92 and the electronics package 14. Leads 76 for the secondaryinductive coil 16 are attached to gold pads 78 on the ceramic substrate60 using thermal compression bonding, and are then covered in epoxy. Thejunction of the secondary inductive coil 16, thin film lead 10, andelectronics package 14 are encapsulated with a silicone overmold 90 thatconnects them together mechanically. When assembled, the hermeticelectronics package 14 may sit an arbitrary distance away from the endof the secondary inductive coil.

Since the implant device may be implanted just under the scalp it ispossible to irritate or even erode through the scalp. Eroding throughthe scalp leaves the body open to infection. We can do several things tolessen the likelihood of scalp irritation or erosion. First, it isimportant to keep the overall thickness of the implant to a minimum.Even though it may be advantageous to mount both the electronics package14 and the secondary inductive coil 16 on the cranium just under thescalp, the electronics package 14 is mounted higher than, and at adistance laterally displaced from, the secondary inductive coil 16. Inother words the thickness of the secondary inductive coil 16 andelectronics package should not be cumulative.

It is also advantageous to place protective material between the implantdevice and the scalp. The protective material can be provided as a flapattached to the implant device or a separate piece placed by the surgeonat the time of implantation. Adding material over the device promoteshealing and sealing of the wound. Suitable materials include Dacron,Teflon (polytetraflouroethylene or PTFE), Goretex (ePTFE), Tutoplast(sterilized sclera), other processed tissue, Mersilene (Polyester) orsilicone.

Referring to FIG. 8, the package 14 contains a ceramic substrate 60,with metallized vias 65 and thin-film metallization 66. The package 14contains a metal case wall 62 which is connected to the ceramicsubstrate 60 by braze joint 61. On the ceramic substrate 60 an underfill69 is applied. On the underfill 69 an integrated circuit chip 64 ispositioned. On the integrated circuit chip 64 a ceramic hybrid substrate68 is positioned. On the ceramic hybrid substrate 68 passives 70 areplaced. Wirebonds 67 are leading from the ceramic substrate 60 to theceramic hybrid substrate 68. A metal lid 84 is connected to the metalcase wall 62 by laser welded joint 63 whereby the package 14 is sealed.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably, the secondary inductive coil 16 is madefrom wound wire. Alternately, the secondary inductive coil 16 may bemade from a flexible circuit polymer sandwich with wire traces depositedbetween layers of flexible circuit polymer. The electronics package 14and secondary inductive coil 16 are held together by the molded body 18.The molded body 18 holds the electronics package 14 and secondaryinductive coil 16 end to end. The secondary inductive coil 16 is placedaround the electronics package 14 in the molded body 18. The molded body18 holds the secondary inductive coil 16 and electronics package 14 inthe end to end orientation and minimizes the thickness or height abovethe sclera of the entire device.

Referring to FIGS. 9 and 10, thin-film metallization 66 is applied toboth the inside and outside surfaces of the ceramic substrate 60 and anASIC integrated circuit chip 64 is bonded to the thin film metallizationon the inside of the ceramic substrate 60.

The inside thin film metallization 66 includes a gold layer to allowelectrical connection using wire bonding. The inside film metallizationincludes preferably two to three layers with a preferred gold top layer.The next layer to the ceramic is a titanium or tantalum, or mixture oralloy thereof. The next layer is preferably a palladium or platinumlayer, or an alloy thereof. All these metals are biocompatible. Thepreferred metallization includes a titanium, palladium, and gold layer.Gold is a preferred top layer because it is corrosion resistant and canbe cold bonded with gold wire. The outside thin film metallizationincludes a titanium adhesion layer and a platinum layer for connectionto platinum electrode array traces. Platinum can be substituted bypalladium or a palladium/platinum alloy. If gold-gold wire bonding isdesired a gold top layer is applied.

The three layer stack of metallization consists of an adhesion layer,barrier layer, and a bonding layer. The adhesion layer is a metal bestsuited to bond with the ceramic. Titanium is a good adhesion layermaterial. Titanium is active enough to bond with ceramics, but stillnoble enough to be bio-compatible. Alternative adhesion layers arechromium or tungsten. Both bond better, but are less bio-compatible. Anon-biocompatible adhesion layer may be used if it is adequatelyisolated from the body.

The center layer is a barrier layer. The preferred barrier layer forexternal traces is platinum, while palladium is the preferred barrierlayer for internal traces. The barrier layer prevents, or reducesmigration of the adhesion layer and bonding layer due to heat from thebrazing process. Migration of the layers reduces the effectiveness ofeach layer. Other possible barrier layers are ruthenium, rhodium,molybdenum, or iridium. All of these materials are rare and expensive.Iridium is the only one that is reasonably biocompatible.

The top layer is the bonding layer for bonding electrical connections.Gold is the preferred bonding layer. On the inside metallization,electrical circuits are flip-chip bonded, or wire-bonded to the goldbonding layer. On the outside, the coil 16 is compression bonded to thegold bonding layer. Alternatively, a thermo-compression process may beused. The electrode array cable is attached through a platinum epoxypaste. In this case, a gold bonding layer is counterproductive. Sincethe barrier layer is platinum, the gold bonding layer is etched from thearray bond pads, allowing for a platinum to platinum bond.

Preferably, the layers are sputtered on the ceramic with the adhesionlayer 500 to 1000 angstrom, the barrier layer 5000 angstrom, and thebonding layer 2000 angstrom. The traces are patterned with photo-resistand wet etched with potassium iodide. Additionally, the bonding layermay be electroplated to ten microns for a better bonding surface.Alternatively, a lift off process may be used. If a lift off process isused, care must be taken to completely clean photo-resist from traceareas to provide for good adhesion. The metallization includes capturepads to improve alignment with the vias.

It should also be noted that the thin film metallization 66 includes asingle ring 67 completely around the interior or top surface of thesubstrate 60. When brazing, it common for braze material to flow furtherthan desired, which is called braze run out. A single ring around thecircumference of the substrate 60, sputtered and patterned as part ofthe thin film metallization, provides a dam to prevent braze run outfrom contacting and shorting the traces used for electrical redirection.

FIG. 10B shows the locations of the vias or feedthroughs 65 on thesubstrate 60 prior to sputtering the thin film metallization 66. Thefollowing discussion is directed to a method and apparatus suitable forforming hermetic electrical vias or feedthroughs in a ceramic sheet (orsubstrate) having a possible thickness of ≤40 mils, for the constructionof the substrate 60, with metallized vias (feedthroughs) 65. Themetallization includes capture pads to improve alignment with the vias.

Electrical feedthroughs in accordance with the present writing areintended to function in corrosive environments, e.g., in medical devicesintended for implantation in a patient's body. In such applications, itis generally critical that the device housing be hermetically sealed,which, of course, requires that all feedthroughs in the housing wallalso be hermetic. In such applications, it is also generally desirablethat the weight and size of the housing be minimized and that allexposed areas of the housing be biocompatible and electrochemicallystable. Biocompatibility assures that the implanted device has nodeleterious effect on body tissue. Electrochemical stability assuresthat the corrosive environment of the body has no deleterious effect onthe device. Ceramic and platinum materials are often used in implantablemedical devices because they typically exhibit both biocompatibility andelectrochemical stability.

Embodiments constructed in accordance with the present disclosure areable to achieve very high feedthrough density. For example, inapplications where miniaturization is important, the feedthrough pitch,i.e., center-to-center distance between adjacent feedthroughs, may befrom 10 mils to 40 mils.

Attention is initially directed to FIGS. 11 and 12 which depict apreferred feedthrough assembly 108 in accordance with the presentdisclosure comprising a thin ceramic sheet 110 of ceramic materialhaving multiple electrical feedthroughs 112 extending therethrough,terminating flush with the upper and lower surfaces 114, 116 of thesheet 100. The sheet 100 typically comprises a portion of a housing (notshown) for accommodating electronic circuitry. The feedthroughs 112function to electrically connect devices external to the housing, e.g.,adjacent to surface 114, to electronic circuitry contained within thehousing, e.g., adjacent to surface 116. “Thin ceramic sheet” as usedherein refers to a sheet having a finished thickness dimension of ≤40mils, i.e., 1 mm. The apparatus in accordance with the disclosure isparticularly suited for use in corrosive environments such as in medicaldevices implanted in a patient's body.

The present disclosure is directed to providing electrical feedthroughsthat are compatible with thin ceramic sheets (or substrates) having afinished thickness of s 40 mils, and with feedthroughs that arehermetic, biocompatible, and electrochemically stable. In one exemplaryembodiment, the ceramic sheet 110 may be formed of 90% aluminum oxide(AlO₂) and the feedthroughs 112 may have a diameter of ≤20 mils and maybe composed of paste containing, for example, platinum.

Attention is now directed to FIGS. 13 and 14A-14M which depict thepossible process steps for fabricating the finished feedthrough assembly108 illustrated in FIGS. 11 and 12.

Initially, a green ceramic sheet/tape/substrate 120 (FIG. 14A), formed,for example, of >90% aluminum oxide (AlO₂) is selected as represented bystep 121 in FIG. 13. In an exemplary embodiment, the sheet 120 may havea thickness of 40 mils or less. “Green ceramic sheet/tape/substrate” asused herein refers to an unfired ceramic sheet, tape or substrate.

Via holes 126 are formed into the sheet 120 as represented by FIGS.14B-14C and step 128 in FIG. 13. In an exemplary embodiment, each viahole 126 may be punched into the sheet 120 using, for example,programmable punch tool 127. In one exemplary embodiment, a plurality ofvia holes 126 may be punched at the same time. It is to be understoodthat other methods may be used to form via holes 126. For example, viaholes 126 may be formed using solvent etching, laser ablation, and/orvia holes 126 may be drilled.

Step 137 of FIG. 13 calls for selecting a conductive thick-film paste117 to fill in via holes 126 depicted in FIG. 14C. “Thick-film paste” asused herein refers to a material containing inorganic particlesdispersed in a vehicle comprising an organic resin and a solvent. Typesof different pastes are disclosed in U.S. Pat. No. 5,601,638, thedisclosure of which is incorporated herein by reference.

In one exemplary embodiment, a stencil printing with vacuum pull downprocess may be used to fill via holes 126 with the conductive paste 117as represented by FIGS. 14D-14E and step 139 in FIG. 13. During thestencil printing with vacuum pull down process, the sheet 120 may besandwiched between a stencil layer 119 and a vacuum base 180. As asqueegee 118 roles the conductive paste 117 across the stencil layer119, a vacuum chuck 181 of the vacuum base 180 pulls the conductivepaste 117 through holes 182 of the stencil layer 119 and into the viaholes 126 as shown in FIGS. 14D-14E.

Step 140 of FIG. 13 calls for determining if additional green ceramicsheet/tape/substrates with paste filled via holes are required. Ifadditional green ceramic sheet/tape/substrates with paste filled viaholes are required (“Yes” in step 140), steps 121, 128, 137 and 139 arerepeated. If additional green ceramic sheet/tape/substrates with pastefilled via holes are not required (“No” in step 140), step 141 of FIG.13 is performed.

Upon completion of the stencil printing with vacuum pull down processand step 140, the sheet 120 with via holes 126 filled with conductivepaste 17 shown in FIG. 14F may go through a multilayer laminationprocess as represented by FIGS. 14G-14H and step 141 in FIG. 13.

In the multilayer lamination process, the sheet 120 of FIG. 14F may belaminated with, for example, sheets 191 and 192 as shown in FIG. 14G.The sheets 191 and 192 may contain conductive paste filled vias 126 thatare similar to the conductive paste filled vias 26 of the sheet 120 andthe sheets 191 and 192 may be formed using steps 121, 128, 137 and 139of FIG. 13 as described above.

During the multilayer lamination process, a) the sheets 120, 191 and 192are stacked on top of each other with conductive paste filled vias 126of each sheet being aligned on top of each other; b) stacked sheets 120,191 and 192 are sandwiched between two unpunched green ceramicsheets/tapes/substrates 195 and 196; and c) the sheets 120, 191 and 192and the sheets 195 and 196 are laminated together using a heat press 198to create a/the laminated substrate 200 shown in FIG. 14I.

Although FIGS. 14G and 14H laminate three sheets 120, 191 and 192 withconductive paste filled vias 126, one skilled in the art can appreciatethat this disclosure is not limited to three sheets and that a singlesheet 120 with conductive paste filled vias may be laminated togetherwith the sheets 195 and 196 without the additional sheets 191 and 192.Although FIGS. 14G and 14H laminate three sheets 120, 191 and 192 withconductive paste filled vias 126, one skilled in the art can appreciatethat this disclosure is not limited to three sheets and that additionalsheets with conductive paste filled vias may also be laminated togetherwith sheets 120, 191 and 192.

Step 144 of FIG. 13 calls for the laminated substrate 200 to be fired.Firing of the laminated substrate 200 encompasses different aspects offorming bonds in ceramic (evaporation, binder burnout, sintering, etc.).The unpunched ceramic layers 195 and 196 of the laminated substrate 200help to constrain the conductive paste within via holes 126 and allowfor compression during the firing step 144. The unpunched ceramic layers195 and 196 of the laminated substrate 200 also help to isolate theconductive paste filled vias 126 from the firing atmosphere during thestep 144 which may be the key to hermetic and low resistance pastefilled vias 126. An exemplary firing schedule includes ramping thelaminated substrate 200 of FIG. 14I up to 600° C. at a rate of 1°C./minute, then ramping up to 1600° C. at a rate at 5° C./minute,followed by a one hour dwell and then a cool-to-room-temperatureinterval.

During the firing and subsequent cooling during the step 144, theceramic material of the laminated substrate 200 shrinks therebyshrinking via holes 126 around the paste 117 to form a seal. The finealuminum oxide suspension permits uniform and continuous sealing aroundthe surface of the paste 117. Additionally, at the maximum firingtemperature, e.g., 1600° C., the paste 117 being squeezed by the ceramicexhibits sufficient flow to enable the paste 117 to flow and fill anycrevices in the ceramic. This action produces a hermetic paste/ceramicinterface. Furthermore, the firing step 144 may also cause hermeticitythrough bonding mechanisms like, for example, sintering, glassmelt/wetting, alloying, compounding, and/or diffusion solutionformation.

“Sintering” as used herein is a term used to describe the consolidationof the ceramic material during firing. Consolidation implies that withinthe ceramic material, particles have joined together into an aggregatethat has strength. The term sintering may be used to imply thatshrinkage and densification have occurred; although this commonlyhappens, densification may not always occur. “Sintering” is also amethod for making objects from powder, by heating the material (belowits melting point) until its particles adhere to each other. “Sintering”is traditionally used for manufacturing ceramic objects, and has alsofound uses in such fields as powder metallurgy. “Alloying” as usedherein refers to an alloy that is a homogeneous hybrid of two or moreelements, at least one of which is a metal, and where the resultingmaterial has metallic properties. “Compounding” as used herein refers toa chemical compound that is a substance consisting of two or moreelements chemically-bonded together in a fixed proportion by mass.“Diffusion solution formation” as used herein refers to the net movementof particles from an area of high concentration to an area of lowconcentration. A solid solution is a solid-state solution of one or moresolutes in a solvent. Such a mixture is considered a solution ratherthan a compound when the crystal structure of the solvent remainsunchanged by the addition of solutes, and when the mixture remains in asingle homogeneous phase. Also, the firing step 144 may also causesolidification of the metalized vias 126 and the ceramic material of thelaminated substrate 200 to prevent leaks.

Step 148 of FIG. 13 calls for lapping or grinding the upper and lowersurfaces of the fired laminated substrate 200 to remove materials 150and 151, depicted in FIG. 14J, in order to expose the upper and lowerfaces of the metalized vias 126. The upper and lower surfaces of thefired laminated substrate 200 may also go through the polishing step 149so that the metalized vias 126 are flush with the surrounding ceramicmaterial.

After lapping and/or grinding, the fired laminated substrate 200 may besubjected to a hermeticity test, e.g., frequently a helium (He) leaktest as represented by step 156 in FIG. 13.

In one exemplary embodiment, sheet/substrate 120 may contain severalpatterns 124A-D of the via holes 126 as shown in FIG. 14L. In thisexemplary embodiment, the fired laminated substrate 200 would containseveral patterns 124A-D of the metal filled via holes 126 and the firedlaminated substrate 200 would be subjected to a singulation or dicingstep 158 to provide multiple feedthrough assemblies 160A, 160B, 160C,160D, shown in FIG. 14M.

Although some embodiments described above employ a ceramic sheet of >90%aluminum oxide (AlO₂), alternative embodiments may use other ceramicmaterials, e.g., zirconium. Because the firing temperature of theceramic can be tailored within certain limits, the conductive paste 17may comprise any of the noble metals and/or any of the refractorymetals, for example, platinum, titanium, gold, palladium, tantalum,niobium.

The package of the present invention can applied to many uses in themedical device industry. The present invention applies the package toneural sensing for motor control and stimulation for sensory feedback.

FIG. 15 shows the application of the package of the present invention todeep brain stimulation, as shown in FIG. 2A, but in further detail. Dueto the low profile of the package, the package 214 can be implanted in ahollowed out portion of the cranium 208. The hollowed out portion may gopart way through the cranium 208, leaving part of the bone under thepackage 214. Alternatively, the hollowed out portion may extend throughthe cranium and the package 214 rests on the durra 206. This protectsthe package 214, allows the package 214 to be placed close to thesensing or stimulation site, and avoids visible protrusions on the head.The package 214 contains a ceramic substrate 260 with metallized vias265 and thin-film metallization 266. The package 214 contains a metalcase wall 262 which is connected to the ceramic substrate 260 by brazejoint 261. On the ceramic substrate 260 an underfill 269 is applied. Onthe underfill 269 an integrated circuit chip 264 is positioned. On theintegrated circuit chip 264 a ceramic hybrid substrate 268 ispositioned. On the ceramic hybrid substrate 268 passives 270 are placed.Wire bonds 267 are leading from the ceramic substrate 260 to the ceramichybrid substrate 268. A metal lid 284 is connected to the metal casewall 262 by laser welded joint 263, whereby the package 214 is sealed.In addition, a rechargeable battery 280 is placed within the package 214to allow the deep brain stimulator to operate without external power. Athin film array cable 212 leads to an electrode array 210 for sensingstimulation of brain tissue 204. A coil 216 is placed close to the scalpto receive inductive power and data from an external coil (not shown) toprogram the electronics and recharge the battery 280.

Also, a cover 282 such as Dacron mesh may be used to hold the package216 in place. The cover 282 may be glued or screwed to the cranium. Itshould be noted that the package 214 is placed with the delicate ceramicsubstrate 260 protected with the more durable metal lid 284 just beneaththe scalp.

FIG. 16 shows the preferred method of bonding the substrate 60 to theflexible thin film lead 10 using electrically conductive adhesive 381,such as a polymer, which may include polystyrene, epoxy, or polyimide,and which contains an electrically conductive particulate of selectbiocompatible metal, such as platinum, iridium, titanium, platinumalloys, iridium alloys, or titanium alloys in dust, flake, or powderform.

In FIG. 16, step A, the substrate 60, and the input/output contacts 322are prepared for bonding by placing conductive adhesive 381 on theinput/output contacts 322, at the ends of the thin film metallizationtrace 66. In step B, the flexible thin film lead 10 is preferablyprepared for bonding to the substrate 60 by placing conductive adhesive381 on bond pads 332. Alternatively, the adhesive 381 may be coated withan electrically conductive biocompatible metal. The flexible thin filmlead 10 contains the flexible electrically insulating substrate 338,which is preferably comprised of polyimide. The bond pads 332 arepreferably comprised of an electrically conductive material that isbiocompatible when implanted in living tissue, and are preferablyplatinum or a platinum alloy, such as platinum-iridium.

FIG. 16, step C illustrates the cross-sectional view A-A of step B. Theconductive adhesive 381 is shown in contact with and resting on the bondpads 332. Step D shows the hybrid substrate 60 in position to be bondedto the flexible thin film lead 10. The conductive adhesive 381 providesan electrical path between the input/output contacts 322 and the bondpads 332. Step C illustrates the completed bonded assembly wherein theflexible thin film lead 10 is bonded to the substrate 60, therebyproviding a path for electrical signals to pass to the living tissuefrom the package 14. The assembly has been electrically isolated andhermetically sealed with adhesive underfill 380, which is preferablyepoxy.

Alternatively, the package may be constructed from a single or multiplelayers of a single or multiple polymers, including but not limited tobiocompatible epoxies, Parylene, polyimide, silicone, PDMS, PGA, Teflon,PEG, and PMMA.

To this package a polymer-based electrode cable 330, array 331, and abond pad region 332 are attached. The cable, bond pad region, and arrayis a single integrated unit that forms the flexible thin film lead 10shown in FIG. 17 with bond pads 335 at the proximal end and electrodes333 at the distal end. The cable and array unit is composed of a basepolymer 336 layer, one interlayer of patterned metal 337 (or a stack upof metals) comprising traces 33 and electrodes 333, and a top polymerlayer 338 that is patterned to expose the pads and electrodes, butinsulate the traces. Such a cable and array may be referred tocollectively as a thin film lead 10 and may be manufactured in a mannerdisclosed in U.S. patent application Ser. Nos. 11/207,644 and 11/702,735incorporated herein by reference. Alternatively, the lead may consist ofmore than one metal interlayer and corresponding additional polymerinterlayers so that the thin film lead may be considered a multilayerstructure. In a more preferable embodiment, the polymer employed for thebase layer, inter layer(s), and top layer is polyimide. Other possiblepolymers include Parylene, silicone, Teflon, PDMS, PMMA, PEG, andothers.

The thin film lead consists of at least 30 independent pads, traces, andelectrodes, or preferably at least 50, 60, 100, or 200 pads, traces, andelectrodes. The advantages of having so many independent channels isthat sensing or stimulation may be performed at several sites at onceresulting in better therapy, or if combined with asensing/recording/feedback mechanism either at the time of surgicalimplantation or throughout the life of the implant, optimal electrodesmay be selected for sensing or stimulation, reducing the total poweroutput required, which reduces power consumption and may also minimizethe occurrence of side effects.

The electrodes of the thin film lead are preferably biocompatible andcapable of sensing or delivering stimulation charge densities of atleast 0.1 mC/cm². One metal often employed to deliver such chargedensities is platinum but other noble metals and some metal oxides andnitrides may be used. Since it is an advantage of the current inventionto have numerous electrodes, it may be necessary in some applications,where the array is to be small, to have the stimulating electrodes besmall, preferably less than about 500 um, or less than 250 um, or lessthan 200, 200, 50, 25 and 10 um. For such small electrodes, therapeuticdoses of electrical current are likely to exceed 0.1 mC/cm², and in suchcases it may be desirable to employ electrode materials that permit thesafe use of higher charge densities. Two such electrode materials areplatinum gray and super iridium oxide, disclosed in U.S. Pat. No.6,974,533 and U.S. patent application Ser. No. 10/655,772 incorporatedherein by reference.

The thin film lead 10 is intended to penetrate the cranium 7 through asurgical opening in the cranium and dura 12 and sit on the surface ofthe brain (FIG. 2B.) such that the array 331 of electrodes 333 is at ornear the intended target for sensing or stimulation, or the thin filmlead may penetrate into the brain (FIG. 2A.) so that the array ofelectrodes reaches the intended target for sensing or stimulation deepwithin the brain. Alternatively, the thin film lead may be placed on aninner surface of the brain between two or more lobes.

The thin film lead in one embodiment may be substantially flat andplanar for its entire length. In other embodiments it may be desirableto shape all, much, or some of the lead. For example, it may bedesirable to curve a region of the lead along its longitudinal axis intoa columnar structure that is more rigid than the planar array (FIG.18A). In such a scenario the edges of the folded structure may or maynot overlap and could be held in place with a binding material such assilicone 343 and 344. This binding material could be beaded along theedge or applied to the entire edge or in distinct locations. It may alsobe desirable to have a sharpened tip 340 for this structure such that itmay be used to penetrate the brain, and/or an introducer 341 that may beinserted into the columnar structure and used to guide the lead intoplace. In another embodiment (184B), where the array is intended to beplaced on the surface of the brain, either for recording or stimulation,it may be desirable to shape the array region of the lead to conform tothe intended target. Such shaping may be accomplished using molding orthermo-forming of the thermoset or thermoplastic polymers used in thelead. In any case where 3D shaping of the lead or components of the leadare desired, it may be desirable to include physical features in theplanar thin film lead (such as cut outs 342) that facilitate thisshaping step. These cutouts could have a variety of shapes such as arounded feature 345 or a slit 346.

In an alternative embodiment (shown in FIG. 23), it may be desirable toattach an array of penetrating electrodes 13 to the package(s), eitherin place of the thin film lead, or in addition to the thin film array.Such a penetrating array is composed of electrodes of an aspect ratioand sharpness suitable for allowing the array to penetrate the duraand/or brain in order to contact neurons that are not at the brain'ssurface. Such a penetrating array may be more suitable for recordingneuronal activity, or sensing a physiological parameter than a surfacethin film lead or a penetrating thin film lead. Additionally, such anarray may be able to stimulate cells within the brain more efficientlythan the thin film leads. It may also be desirable to use a penetratingarray for sensing/recording and a surface thin film lead for sensing orstimulation. It may be also be desirable to use a penetrating array forsensing and/or recording and/or stimulation and a surface thin film leadfor sensing and/or recording and/or stimulation. FIG. 23A shows an arrayof penetrating electrodes penetrating the brain in one location with asurface thin film lead in another location, while FIG. 23B shows bothtypes of arrays in a similar location. FIG. 23C shows an embodiment thatuse a penetrating thin film lead in conjunction with a surface thin filmlead.

The array and/or portions of the cable which comprise the thin film leadmay be fixated to tissue (scalp, cranium, brain matter, or dura) usingseveral possible techniques. One fixation method would employ a tacksimilar to that disclosed in U.S. patent application Ser. No.09/975,427, incorporated herein by reference. In one embodiment the tackwould penetrate through a hole in the array 345 or cable intoneighboring tissue. In another embodiment at least two tacks wouldpenetrate at least two holes in the cable and/or array. A biocompatibleglue or adhesive may be used to fix the array and/or cable in place.This glue or adhesive may be preferentially reversible through theadministration of light, heat, energy, or a chemical agent in order toallow rapid removal of the thin film lead. Electro-tacking, whereby oneor more electrodes are sacrificed to fix the array to tissue bydischarging a significant electrical current through the electrode, mayalso be employed. This process may also be reversible. Alternatively,physical features may be constructed in the polymer thin film lead thatpermit anchoring of the lead to adjacent tissue. Such features may beone or more protuberances that anchor into tissue when pressure isapplied or holes that permit tissue growth through and around the lead.In another embodiment, regardless of the method of array attachmentused, it may be desirable to attach the array to the inside (brain side)surface of the dura with the electrodes facing the brain. In thisembodiment it may be necessary to put a spacer between the array and thedura in order to force the electrodes to be proximal to the brain tissuetarget for sensing or stimulation. One such spacer is made from abiocompatible sponge-like material. Additionally, one or more handletype structures 339 may be added to the thin film lead to permit holdingof the lead or a region of the lead using surgical tools such asforceps, or end gripping forceps.

Attachment of the bond pad region 332 of the thin film lead 10 to thepackage 14 is carried out using a method or methods similar to thosedisclosed in U.S. Pat. Nos. 7,142,909 and 7,211,103 incorporated hereinby reference.

One or more reference or return electrodes must be provided in order toprovide a return for the stimulation current. A feature of the presentinvention is that the return electrode(s) be provided in or on thebrain. The return electrodes may be contained on the thin film lead(s)containing the sensing or stimulation electrodes or they may be on theirown independent leads that may or may not be thin film leads.Alternatively, the lid and/or other metal components of the package(s)may be used to provide an electrical return.

A coil 16 is also attached to the package 14. This coil permitsradio-frequency communication between the implant and an externalapparatus. This coil may receive power and data signals from theexternal apparatus and may send information about the implant or asensed physiological condition out to the external apparatus. The coilmay be attached to the package via wire leads 5 or alternatively may beattached to the polymer thin film lead 10 via bonding of the coil wiresto additional bond pads in the polymer. Or in another embodiment, thecoil may be integrated into polymer thin film lead as a patterned metalcoil made from the same or a different metal stack up as that employedin the rest of the lead. The coil profile and shape is such that thescalp may rest of top of the coil without being irritated. Thus the coilis low profile with rounded edges and is preferably encased in abiocompatible soft polymer mold such a silicone or other elasticpolymers. The coil(s) facilitates transmission of data between theimplant and the external system and possibly between implanted coils. Inthe case of a device without a rechargeable battery the coil is alsoused to receive power from an external source. It is a feature of thepresent invention that where the implanted coil(s) is to receive bothpower and data, at least two different carrier frequencies are used; onefor power transmission and one or more for data transmission.

In another embodiment of the present invention, a sensor is employed inthe device where the sensor is contained within the package, and/or onthe thin film lead. As well, the electrodes (either on a penetratingarray/lead or on a thin film surface lead) may be used to recordelectrical activity in the brain, or measure electrical properties ofthe entire system (i.e. impedance, or voltage waveforms). The outputfrom such a sensor/recorder/measurement system may be used by theimplanted electronics to determine a course of action, or theinformation may be telemetered out to the external system to beprocessed in order to determine a parameter of interest. The externalsystem determines a course of action if necessary and telemeters thatdata back to the implant. Optionally, the external system may telemeterthe calculated parameter value(s) back to the implant for subsequentdecision making.

In another embodiment of the present invention (FIG. 19), it may bedesirable to countersink the package 14 into the cranium 7 in order toprotect the device from damage due to an external blow to the head or toprevent irritation of the scalp (shown in FIG. 19A). It may be desirableto turn the package upside down in such a configuration so that the thinfilm lead comes out on the surface of the cranium (as shown). Also, itmay be desirable to countersink the coil 16 in the cranium 7 for thesame reasons. Although a thin film multi-electrode lead is shownpenetrating the brain in this figure, it is possible that the lead mayrest on the surface of the brain or between lobes of the brain. Althoughno flange or tabs are shown on the package or coil in this figure, it isimplied that such fixation features may be present.

In another embodiment of the present invention (FIG. 20), it may bedesirable to have the package 14 be of such a height that it justprotrudes through a hole made in the cranium 7, but not through the dura8. Again, this may protect the device from harm and reduce irritation ofthe scalp. Additionally, such an architecture reduces the number ofincisions in the cranium as a separate orifice for the lead 10 is notrequired. The coil may still rest on the outside of the cranium (FIG.20A) or under the cranium (FIG. 20B) as required.

Although specific combinations of package, coil, and thin film lead,and/or penetrating array location are shown in FIGS. 2, 19 and 20, it isunderstood that these architectures are not limiting in any sense andthat any permutation of combination of these architectures is alsodisclosed in this invention. Similarly, it is understood that there isno reason to limit the implant architecture to containing only one of acoil, package, and thin film lead. The present invention may consist ofany number of those components disposed at different positions in thehead as previously described. An example is provided in FIG. 21. In thisembodiment there are 2 packages 14 and 15, one, a primary controller,which houses electronics for the implant, and another secondary packagewhich primarily contains a battery but may alternatively contain someadditional electronics or may only contain additional electronics. Twothin film leads 10 are attached to the primary controller. One of theseleads may penetrate the brain while the other sits on a surface, or bothmay penetrate or both may sit on the surface. Two coils 16 and 17 areattached to the primary controller perhaps for redundancy or perhaps topermit easier collocation of the external communication unit.

It is a feature of this embodiment that the secondary package isconnected to the primary controller using the same polymer based cablestructure as that employed for the two thin film leads 350. This isshown more clearly in FIG. 21C, which indicates that the entire polymerbased thin film structure, including both leads all interconnectionsrequired for multiple packages and coils, may be provided in one piece.Alternatively, it may be desirable to have the secondary package attachto the primary controller using a connector that can be connected orunconnected in situ. An example of such a connector 351 is shown in FIG.21C. Here, wire leads from the secondary package plug into a connectoron the primary controller facilitating, potentially, easy replacement ofthe secondary feature (say a battery). Other connector embodiments willbe readily apparent to one of normal skill in the art. The primaryfeature of such a connector is that it provides for minimal electricalcurrent leakage (at least less than 1 uA/s, more preferably less than0.1 uA/s or even 0.01 uA/s).

Although FIG. 21 shows one device architecture it should not be limitingas it may be appreciated that any number of coils, packages, and leadsmay be used in any combination, and that any polymer based structure(s)used to connect the components do not necessarily need to bemanufactured in one integrated unit. As well, the physical locations ofthe components in and on or under the cranium may also vary.

Similarly, it is an aspect of the present invention that a thin filmlead may not be required. Instead multiple electrodes may be formed inthe package itself. One such embodiment is shown in FIG. 20C, where thepackage extends through the cranium and dura and makes contact with thesurface of the brain with multiple electrodes.

It is also an aspect of the present invention that the coil need not beremote from a package but may alternatively be contained in a package.

Another aspect of the present invention includes coating the package(s),and/or coil(s), and or thin film lead(s) with materials that enhancebiocompatibility, resistance to corrosion, tissue growth, neural tissuegrowth, and or coatings that deliver pharmaceutical agents that enhancedevice function or disease treatment.

Another embodiment of the present invention includes the addition of oneor more integrated circuits or chips that are coated in a biocompatibleand hermetic thin film package of the type disclosed in U.S. Pat. Nos.7,127,286, 7,190,051, and patent application Ser. Nos. 11/406,743,11/343,170, incorporated herein by reference. A chip or chips coated insuch a way enables new device architectures that benefit from areduction in the size of the device and/or a further increase in thenumber of electrodes.

Examples of these new architectures are shown in FIG. 22. In FIG. 22A, acoated chip 49 (a demultiplexer, for example) is added to the thin filmlead near the array. In this way, the traces in the lead can be used toaddress more than a single electrode. For example, if the ceramicfeedthrough permits at most 68 vias 16 but perhaps 480 electrodes aredesired for the device, then 60 traces (along with some power andcontrol lines) may be routed to the chip 49 which can perform 1:8demultiplexing of the input signals to high density electrode outputsalso located on the chip. An example is shown in FIG. 22D and E(although 8:1 demultiplexing is not necessarily maintained in thedrawing). It should be obvious to one of reasonable skill in the artthat more than one coated chip may be used in such an architecture, andthat coated discrete electronic components may also be employed. Inanother embodiment, the demultiplexing function may be moved to insideone or more of the packages. In this scenario, the ceramic may containenough feedthroughs to address each electrode individually, but theelectronics may not have enough drivers to drive current through eachelectrode independently. In this case the demultiplexing may occurwithin in the package.

Alternatively, it may be possible to place all of the requiredelectrical circuitry on a single coated chip or multiple coated chipswith or without demultiplexing such that the chip(s) can be placed underthe cranium and or dura as shown in FIG. 22B. In this case the chip isshown deep within the brain but it may be appreciated by anyone skilledin the art that the chip may also be on a surface of the brain or dura.In this case only data and or power from an implanted coil and/orbattery located on the cranium (as shown), in the cranium, or under thecranium need be routed to the chip along a thin film lead.Alternatively, even the coil may be integrated into the coated chip suchthat no additional component is required, as shown in FIG. 22C. In sucha scenario it may or may not be desirable to have the chipinterconnected to a polymer lead of similar size as the chip, such leadcontaining the electrodes that interface with the tissue. This step maybe required to tailor the physical properties of the tissue interface orto permit manufacturing processes for the electrodes (for exampleelectro-plating of platinum gray) that might not otherwise be possibleif the electrodes were placed directly on the chip.

Although specific examples of numbers and locations of coils, packages,leads, and chips are shown in the drawings, it is implied that anycombination of numbers of components and their locations that arereasonable extensions from this invention are also included.

In one other embodiment, a package of the type already disclosed in FIG.3 but of very low profile, preferably less than 2 mm, or 1.5 mm, or even1 mm in height, may be used to encase and protect the chip(s) (andpossibly other components) rather than a thin film package. Again,several such packages implanted beneath the dura on the surface of ordeep within the brain may also be desirable.

Referring to FIG. 24, specific target sensing or stimulation areas ofthe brain for the system described include the sensory and motor areas.

This application is a cortically driven motor prosthesis: electrodesimplanted on or in a motor strip, which, when activated, causeinvoluntary movements in the subject. The implant provides control foran external robotic prosthesis—an implant with recording electrodes onor in a pre-motor (forward of motor strip) or motor strip, which sendsdata wirelessly to an external processor which drives a robotic limb(arm, hand, leg, foot) or stimulates muscles in a deinervated arm, hand,leg, foot, face, tongue, etc.

Motor signal neural recorder and a somatosensory prosthesis providingmotor control and external or implantable sensors that respond to

-   -   1. Pressure    -   2. Temperature (heat or cold) or    -   3. Harmful stimuli such as sharp objects which send data to a        processor that then sends the information to an implanted        prosthesis with stimulating electrodes on or in the        somatosensory strip.

The flexible circuit 1 is a made by the following process. First, alayer of polymer (such as polyimide, fluoro-polymers, silicone or otherpolymers) is applied to a support substrate (not part of the array) suchas glass. Layers may be applied by spinning, meniscus coating, casting,sputtering, or other physical or chemical vapor deposition, or similarprocess. Subsequently, a metal layer is applied to the polymer. Themetal is patterned by photolithographic process. Preferably, aphoto-resist is applied and patterned by photolithography followed by awet etch of the unprotected metal. Alternatively, the metal can bepatterned by lift-off technique, laser ablation or direct writetechniques.

It is advantageous to make this metal thicker at the electrode and bondpad to improve electrical continuity. This can be accomplished throughany of the above methods or electroplating. Then, the top layer ofpolymer is applied over the metal. Openings in the top layer forelectrical contact to the electronics package 14 and the electrodes maybe accomplished by laser ablation or reactive ion etching (RIE) orphotolithography and wet etch. Making the electrode openings in the toplayer smaller than the electrodes promotes adhesion by avoidingdelamination around the electrode edges.

The pressure applied against the neural tissue by the flexible circuitelectrode array is critical. Too little pressure causes increasedelectrical resistance between the array and the tissue. It should benoted that where the present invention is described in terms ofapplication to the brain, the techniques described are equallyapplicable to many forms of neural sensing or stimulation. Applicationto the brain requires a convex spherical curve. Application to thecochlea requires a constant curve in one dimension and a spiral curve inthe other. Application to the cerebral cortex requires a concavespherical curve. Cortical recording and stimulation is useful for touchand motor control for limb prostheses.

Common flexible circuit fabrication techniques such as photolithographygenerally require that a flexible circuit electrode array be made flat.Since the brain is spherical, a flat array will necessarily apply morepressure near its edges, than at its center. With most polymers, it ispossible to curve them when heated in a mold. By applying the rightamount of heat to a completed array, a curve can be induced that matchesthe curve of the brain. To minimize warping, it is often advantageous torepeatedly heat the flexible circuit in multiple molds, each with adecreasing radius. FIG. 25 illustrates a series of molds according tothe preferred embodiment. Since the flexible circuit will maintain aconstant length, the curvature must be slowly increased along thatlength. As the curvature 430 decreases in successive molds (FIGS.25A-25E), the straight line length between ends 432 and 434 mustdecrease to keep the length along the curvature 430 constant, where mold25E approximates the curvature of the brain or other desired neuraltissue. The molds provide a further opening 436 for the flexible circuitcable 10 of the array to exit the mold without excessive curvature.

It should be noted that suitable polymers include thermoplasticmaterials and thermoset materials. While a thermoplastic material willprovide some stretch when heated, a thermoset material will not. Thesuccessive molds are, therefore, advantageous only with a thermoplasticmaterial. A thermoset material works as well in a single mold as it willwith successive smaller molds. It should be noted that, particularlywith a thermoset material, excessive curvature in three dimensions willcause the polymer material to wrinkle at the edges. This can causedamage to both the array and the brain. Hence, the amount of curvatureis a compromise between the desired curvature, array surface area, andthe properties of the material.

Referring to FIG. 26, the edges of the polymer layers are often sharp.There is a risk that the sharp edges of a flexible circuit will cut intodelicate tissue. It is advantageous to add a soft material, such assilicone, to the edges of a flexible circuit electrode array to roundthe edges and protect the brain. Silicone around the entire edge ispreferable, but may make the flexible circuit less flexible. So, anotherembodiment, as depicted in FIG. 26, has discrete silicone bumpers orribs to hold the edge of the flexible circuit electrode array away fromthe brain tissue. Curvature 440 fits against the neural tissue to bestimulated, in this case the brain. The leading edge 444 is most likelyto cause damage and is therefore fit with molded silicone bumper. Also,edge 446, where the array lifts off the brain, can cause damage andshould be fit with a bumper. Any space along the side edges of curvature440 may cause damage and may be fit with bumpers as well. It is alsopossible for the flexible circuit cable 10 of the electrode array tocontact the brain. It is, therefore, advantageous to add periodicbumpers along the flexible circuit cable 10.

FIG. 27 depicts a further embodiment of the part of the prosthesis shownin FIG. 26, with a fold A between the flexible circuit electrode array333 and the flexible circuit cable 10. The angle in the fold A alsocalled ankle has an angle of 1°-180°, preferably 80°-120°. The fold Amay be advantageous in reducing tension and enabling a more effectiveattachment of the flexible circuit electrode array.

FIG. 28 shows the flexible circuit electrode array prior to folding andattaching the array to the electronics package. At one end of theflexible circuit cable 10 is an interconnection pad 52 for connection tothe electronics package. At the other end of the flexible circuit cable10 is the flexible circuit electrode array 333. Further, an attachmentpoint 54 is provided near the flexible circuit electrode array 333. Atack (not shown) may be placed through the attachment point 54 to holdthe flexible circuit electrode array 333 to tissue. A stress relief 55is provided surrounding the attachment point 54. The stress relief 55may be made of a softer polymer than the flexible circuit, or it mayinclude cutouts or thinning of the polymer to reduce the stresstransmitted from the tack to the flexible circuit electrode array 333.The flexible circuit cable 10 is formed in a dog leg pattern so thanwhen it is folded at fold 48 it effectively forms a straight flexiblecircuit cable 10 with a narrower portion at the fold 48.

FIG. 29 shows the flexible circuit electrode array after the flexiblecircuit cable 10 is folded at the fold 48 to form a narrowed section.The flexible circuit cable 10 may include a twist or tube shape as well.With a brain prosthesis as shown in FIG. 1, the bond pad 52 forconnection to the electronics package 14 and the flexible circuitelectrode array 333 are on opposite sides of the flexible circuit. Thisrequires patterning, in some manner, both the base polymer layer and thetop polymer layer. By folding the flexible circuit cable 10 of theflexible circuit electrode array 333, the openings for the bond pad 52and the electrodes are on the top polymer layer, and only the toppolymer layer needs to be patterned.

Further, it is advantageous to provide a suture tab 56 in the flexiblecircuit body near the electronics package to prevent any movement in theelectronics package from being transmitted to the flexible circuitelectrode array 333. Alternatively, a segment of the flexible circuitcable 10 can be reinforced to permit it to be secured directly with asuture.

An alternative to the bumpers described in FIG. 26, is a skirt ofsilicone or other pliable material as shown in FIGS. 31, 32, 33 and 34.A skirt 460 covers the flexible circuit electrode array 333, and extendsbeyond its edges. It is further advantageous to include wings 462adjacent to the attachment point 54 to spread any stress of attachmentover a larger area of the brain. There are several ways of forming andbonding the skirt 460. The skirt 460 may be directly bonded throughsurface activation or indirectly bonded using an adhesive.

Alternatively, a flexible circuit electrode array 333 may be layeredusing different polymers for each layer. Using too soft of a polymer mayallow too much stretch and break the metal traces. Too hard of a polymermay cause damage to delicate neural tissue. Hence a relatively hardpolymer, such as a polyimide may be used for the bottom layer and arelatively softer polymer such as a silicone may be used for the toplayer including an integral skirt to protect delicate neural tissue. Thetop layer is the layer closest to the neural tissue.

The simplest solution is to bond the skirt 460 to the back side (awayfrom the tissue) of the flexible circuit electrode array 333 as shown inFIG. 31. While this is the simplest mechanical solution, sharp edges ofthe flexible circuit electrode array 333 may contact the delicatetissue. Bonding the skirt to the front side (toward the brain) of theflexible circuit electrode array 333, as shown in FIG. 32, will protectthe neural tissue from sharp edges of the flexible circuit electrodearray 333. However, a window 462 must be cut in the skirt 460 around theelectrodes. Further, it is more difficult to reliably bond the skirt 460to the flexible circuit electrode array 333 with such a small contactarea. This method also creates a space between the electrodes and thebrain which will reduce efficiency and broaden the electrical fielddistribution of each electrode. Broadening the electric fielddistribution will limit the possible resolution of the flexible circuitelectrode array 333.

FIG. 33 shows another structure where the skirt 460 is bonded to theback side of the flexible circuit electrode array 333, but curves aroundany sharp edges of the flexible circuit electrode array 333 to protectthe brain. This gives a strong bond and protects the flexible circuitelectrode array 333 edges. Because it is bonded to the back side andmolded around the edges, rather than bonded to the front side, of theflexible circuit electrode array 333, the portion extending beyond thefront side of the flexible circuit electrode array 333 can be muchsmaller. This limits any additional spacing between the electrodes andthe tissue.

FIG. 34 shows a flexible circuit electrode array 333 similar to FIG. 33,with the skirt 460, flush with the front side of the flexible circuitelectrode array 333 rather than extending beyond the front side. Whilethis is more difficult to manufacture, it does not lift the electrodesoff the brain surface as with the array in FIG. 32. It should be notedthat FIGS. 31, 33, and 34 show skirt 460 material along the back of theflexible circuit electrode array 333 that is not necessary other thanfor bonding purposes. If there is sufficient bond with the flexiblecircuit electrode array 333, it may advantageous to thin or removeportions of the skirt 460 material for weight reduction.

Referring to FIG. 35, the flexible circuit electrode array 333 ismanufactured in layers. A base layer of polymer 70 is laid down,commonly by some form of chemical vapor deposition, spinning, meniscuscoating, or casting. A layer of metal 72 (preferably platinum) isapplied to the polymer base layer 70 and patterned to create electrodes74 and traces for those electrodes. Patterning is commonly done byphotolithographic methods. The electrodes 74 may be built up byelectroplating or similar method to increase the surface area of theelectrode 74 and to allow for some reduction in the electrodes 74 overtime. Similar plating may also be applied to the bond pads 52 (FIGS.28-30). A top polymer layer 76 is applied over the metal layer 72 andpatterned to leave openings for the electrodes 74, or openings arecreated later by means such as laser ablation. It is advantageous toallow an overlap of the top polymer layer 76 over the electrodes 74 topromote better adhesion between the layers, and to avoid increasedelectrode reduction along their edges. The overlapping top layerpromotes adhesion by forming a clamp to hold the metal electrode betweenthe two polymer layers. Alternatively, multiple alternating layers ofmetal and polymer may be applied to obtain more metal traces within agiven width.

FIG. 36 depicts the flexible circuit array 10 before it is folded andattached to the implanted portion containing an additional fold Abetween the flexible electrode array 10 and the flexible cable 10. Theangle in the fold A also called ankle has an angle of 1°-180°,preferably 80°-120°.

FIG. 37 depicts the flexible circuit array 10 containing an additionalfold A between the flexible electrode array 10 and the flexible cable10. The flexible circuit array as shown in FIGS. 28 and 36 differ by thefold A from each other.

FIG. 38 depicts a flexible circuit array of FIG. 37 with a protectiveskirt 460 and containing an additional fold A between the flexibleelectrode array and the flexible cable. The flexible circuit array asshown in FIGS. 30 and 38 differ by the fold A from each other.

FIG. 41 depicts a top view of a flexible circuit array and flexiblecircuit cable as shown in FIGS. 30, 38, 39, and 40, wherein the array inFIG. 41 contains a slit 80 along the length axis.

FIG. 42 depicts a skirt of silicone or other pliable material as shownin FIGS. 30 to 34. A skirt 460 covers the flexible circuit electrodearray 333, and extends beyond its edges. In this embodiment of thepresent invention, the flexible circuit electrode array contains a slit80 along the lengths axis. Further, according to this embodiment, theskirt of silicone or other pliable material contains preferably at leasttwo attachment points 81, and stress relieves 82 are providedsurrounding the attachment points 81. The attachment points 81 arelocated preferably on the skirt 460 outside the flexible circuitelectrode 333 and are positioned apart as far as possible from eachother. The secondary tack 81 is far enough away from the first tacklocation 54 not to cause tenting. Furthermore, the polyimide iscompletely between the two tacks, which also reduces the possibility oftenting. The wings act like external tabs or strain relieves. Themultiple tacks prevent rotation of the array. Alternatively, thesecondary tack could be placed at an attachment point at 83.

The stress relief 82 may be made of a softer polymer than the flexiblecircuit, or it may include cutouts or thinning of the polymer to reducethe stress transmitted from the tack to the flexible circuit electrodearray 333.

FIG. 43 depicts a flexible circuit array 333 with a protective skirt 460bonded to the back side of the flexible circuit array 333 with aprogressively decreasing radius and/or decreasing thickness toward theedges.

FIG. 44 depicts a flexible circuit array 333 with a protective skirt 460bonded to the front side of the flexible circuit array 333 with aprogressively decreasing radius and/or decreasing thickness toward theedges.

FIG. 45 depicts a flexible circuit array 333 with a protective skirt 460bonded to the back side of the flexible circuit array 333 and moldedaround the edges of the flexible circuit array with a progressivelydecreasing radius and/or decreasing thickness toward the edges.

FIG. 46 depicts a flexible circuit array 333 with a protective skirt 460bonded to the back side of the flexible circuit array 333 and moldedaround the edges of the flexible circuit array and flush with the frontside of the array with a progressively decreasing radius and/ordecreasing thickness toward the edges.

FIG. 47 depicts a side view of the array with a skirt 460 containing agrooved and rippled pad 56A instead of a suture tab 56. This pad 56A hasthe advantage of capturing a mattress suture 57. A mattress suture 57has the advantage of holding the groove or rippled pad 56A in two placesas shown in FIG. 48. Each suture 57 is fixed on the tissue on two places59. A mattress suture 57 on a grooved or rippled mattress 56A thereforeprovides better stability.

FIG. 49 depicts a flexible circuit array 333 with a protective skirt 460bonded to the front side of the flexible circuit array 333 withindividual electrode 13 windows and with material, preferably silicone,between the electrodes 13.

FIG. 50 depicts a flexible circuit array 333 with a protective skirt 460bonded to the back side of the flexible circuit array 333 and moldedaround the edges of the flexible circuit array 333 with individualelectrode 13 windows and with material, preferably silicone, between theelectrodes 13.

FIGS. 51-56 show several surfaces to be applied to one or both sides ofthe flexible circuit array cable. The surfaces are thin films containinga soft polymer, preferably silicone. FIG. 51 shows a flange 15: A flange15 can be a solid film of material containing silicone added to thesurface of the polymer containing polyimide. FIGS. 52-54 show a ladder15A: A ladder 15A is a flange with material removed from centralportions in some shape 19. FIG. 55 shows a skeleton structure 15B. Askeleton 15B is a flange with material removed from perimeter portionsin some shape 21. FIG. 56 shows a structure 15C with beads 23 andbumpers 25. A bead 23 is material added to perimeter portions of thepolymer cable in some shape without material being added on the centralarea. A bumper 25 can be an extended or continuous version of the beadedapproach. Both approaches are helpful in preventing any possible injuryof the tissue by the polymer.

FIG. 57 depicts the top view of the flexible circuit array 333 beingenveloped within an insulating material 11A. The electrode array 333comprises oval-shaped electrode array body 333, a plurality ofelectrodes 13 made of a conductive material, such as platinum or one ofits alloys, but that can be made of any conductive biocompatiblematerial such as iridium, iridium oxide or titanium nitride. Theelectrode array 333 is enveloped within an insulating material 11A thatis preferably silicone. “Oval-shaped” electrode array body means thatthe body may approximate either a square or a rectangle shape, but wherethe corners are rounded. The material body 11A is made of a softmaterial that is compatible with the electrode array body 333. In apreferred embodiment the body 11A made of silicone having hardness ofabout 50 or less on the Shore A scale as measured with a durometer. Inan alternate embodiment the hardness is about 25 or less on the Shore Ascale as measured with a durometer.

FIG. 58 depicts a cross-sectional view of the flexible circuit array 333being enveloped within an insulating material 11A. It shows how theedges of the material body 11A are lifted off due to the contractedradius at the edges. The electrode array 333 preferably also contains afold A between the cable 10 and the electrode array 333. The angle ofthe fold A secures a relief of the implanted material.

FIG. 59 depicts a cross-sectional view of the flexible circuit array 333being enveloped within an insulating material 11A with open electrodes13 and the material 11A between the electrodes 13.

FIG. 60 depicts a cross-sectional view of the flexible circuit array 333being enveloped within an insulating material 11A with open electrodes13. This is another embodiment wherein the electrodes 13 are notseparated by the material 11A but the material 11A is extended.

FIG. 61 depicts a cross-sectional view of the flexible circuit array 333being enveloped within an insulating material 11A with electrodes 13 onthe surface of the material 11. This is a further embodiment with theelectrode 13 on the surface of the material 11A, preferably silicone.The embodiments shown in FIGS. 59, 60, and 61 show a preferred body 11Acontaining silicone with the edges being lifted off from the tissue dueto contracted radius of the silicone body 11A at the edges.

FIG. 62 shows the electrode array 333 and the electrodes 13 enveloped bythe polymer material, preferably silicone 11A in intimate contact withthe tissue B.

The electrode array 333 embedded in or enveloped by the polymermaterial, preferably silicone 11A, can be preferably produced throughthe following steps. The soft polymer material which contains siliconeis molded into the designed shape and partially hardened. The electrodearray 333 which preferably contains polyimide is introduced andpositioned in the partially hardened soft polymer containing silicone.Finally, the soft polymer 11A containing silicone is fully hardened inthe designed shape enveloping the electrode array 333. The polymer body11A has a shape with a decreasing radius at the edges so that the edgesof the body 11A lift off from the brain B.

Referring to FIGS. 63 and 64, small holes are provided on the hardpolymer and subsequently soft polymer containing PDMS is provided on thehard polymer. This way a partial or entire coating or a soft skirt atthe edge is provided by a soft polymer on a hard polymer. The holesprovide a stronger mechanical bond between the hard and soft polymer asthe soft polymer bonds to itself through the holes.

The hard polymer contains polyimide, polyamide, LCP, Peek,Polypropylene, Polyethylene, Paralyne or mixtures or copolymers or blockcopolymers thereof. The soft polymer contains at least one PDMS orsilicone.

FIG. 66 shows a cross-sectional view of a polyimide array coated withPDMS. The cross-section shows two polyimide layer embedding Pt thin filmseed layer and openings for Pt electrodes and bond pads. The electrodescan be Pt gray or other metals as electrodes, such as Pt, Ir, IrOx, Pd,Au, TiN, Ru, Ti, alloys, conducting polymers or layer thereof. Thestructure can be obtained in known procedures as described in US PatentApplications Nos. 2006/0247,754, 2006/0259,112, and 2007/0265,665, theentire content of which is incorporated herein as reference. Thepolyimide array is coated with a soft polymer, which contains PDMS.

The inventors have found that arrays containing only PDMS show metaltrace breakage and/or metal trace/PDMS delaminating. Arrays containingpolyimide only have edges which are too sharp and may not bebiocompatible. Some pinholes or defects on the polyimide layer may causeleakage and corroding of traces.

One way to minimize such problems is to add a PDMS flange (skirt) tocover the edge of the array. During PDMS skirt attachment, some Pt grayelectrodes may be covered which is not desired. Within the skirtwindows, polyimide surface still may be exposed to the brain. A usefulapproach is to make a thinner polyimide array as the center piece, thecore layer, and to coat the entire array with a thin layer of PDMS; andthen open up only the electrode sites for Pt gray plating. This way theelectrodes are not partially or entirely covered by PDMS. Pt grayplating is described in U.S. Pat. No. 6,974,533, the content of which isincorporated herein as reference.

The new flexible array is partially covered by PDMS or has no exposureof polyimide and is a virtual PDMS array with a polyimide center corelayer.

The PDMS coated array eliminates the problem of undesired PDMS coverageon Pt gray electrodes because the Pt gray plating process takes placeafter the PDMS coating is accomplished.

The polyimide layer can be reduced from 6 μm to 3 μm due to theprotection of the PDMS layers. The PDMS top coating can be 5 μm to 20 μmthick. The plated Pt gray electrode is slightly recessed. This helps toimprove current distribution and provide benefits for clinicalstimulation.

To increase the adhesion of PDMS to Polyimide, some small holes on thepolyimide layer (not only on the edges, but also in the centers andaround electrodes) can be provided to achieve anchors for the PDMS asshown in FIGS. 63 and 64.

The center piece material can contain other polymers than polyimide suchas polyamide, LCP, Peek, Polypropylene, Polyethylene, Paralyne ormixtures or copolymers or block copolymer thereof. Parylene, LCP orother materials can also be used for the outer protection layers.

FIG. 66 shows a sequence of steps 1 to 8 for coating a polyimideelectrode with PDMS. The sequence of steps is as follows:

-   -   1. A first PDMS layer having a thickness of 5 μm to 20 μm is        provided;    -   2. A first polyimide layer having a thickness of 2 μm to 4 μm is        provided on the PDMS layer;    -   3. A Pt thin film having a thickness of 0.5 μm to 1.5 μm is        provided on the first polyimide layer (a very thin layer of Ti        or Cr of 500-5000 angstrom can be deposited before and after        this Pt thin-film deposition as an adhesion layer to promote        good adhesion of Pt to polyimide);    -   4. A second polyimide layer having a thickness of 2 μm to 4 μm        is provided on the Pt thin film;    -   5. Holes are provided in the second polyimide layer for bond        pads and electrodes by photoresist pattering or dry or wet etch        off technology;    -   6. A second PDMS layer having a thickness of 5 μm to 20 μm is        provided on the second polyimide layer;    -   7. Holes are provided in the second PDMS layer for bond pads and        electrodes by photoresist pattering or dry or wet etch off        technology;    -   8. Electrodes are prepared in the provided holes by Pt gray or        other metals.

FIG. 67 shows a sequence of steps 1 to 7 for coating a polyimideelectrode with PDMS. The sequence of steps is as follows:

-   -   1. A first PDMS layer having a thickness of 5 μm to 20 μm is        provided;    -   2. A first polyimide layer having a thickness of 2 μm to 4 μm is        provided on the PDMS layer;    -   3. A Pt thin film having a thickness of 0.5 μm to 1.5 μm is        provided on the first polyimide layer (A very thin layer of Ti        or Cr of 500-5000 angstrom can be deposited before and after        this Pt thin-film deposition as an adhesion layer to promote        good adhesion of Pt to polyimide);    -   4. A second polyimide layer having a thickness of 2 μm to 4 μm        is provided on the Pt thin film;    -   5. A second PDMS layer having a thickness of 5 μm to 20 μm is        provided on the second polyimide layer;    -   6. Holes are provided in the second PDMS layer and second        polyimide layer for bond pads and electrodes by photoresist        pattering or dry or wet etch off technology;    -   7. Electrodes are prepared in the provided holes by Pt gray or        other metals.

In yet another embodiment (FIG. 68), it may be desirable to have bothsurface electrodes 333 and penetrating electrodes 313 on the samesurface of the thin film lead 10 as shown in FIG. 68(A). Although analternating pattern of surface and penetrating electrodes is shown, itis understood that the invention is not restricted to this pattern andthat any pattern is available. Also, there is no requirement that equalnumbers of surface and penetrating spike electrodes be employed. FIGS.68B-D, show methods of attachment of individual spike electrodes 313 tothe thin film lead 10 (B) or arrays of spike electrodes 13 to either thepackage 14 or the thin film lead 10 (C and D). The individual spikeelectrodes or the spike electrode array is attached to the flexiblecircuit 10 or the package 14 using a flip-chip bumping process, andepoxy underfilled. In the flip-chip bumping process, bumps containingconductive adhesive placed on the base of individual spike electrodes313 or the bond pads 92 of the spike electrode arrays 13, and bumpscontaining conductive adhesive placed on the electronics package 14 orthe electrodes 333 of the thin film lead 10 are aligned and cured tobuild a conductive connection between the components.

In another embodiment, FIG. 69, it may be desirable to have electrodeson either side of the array. FIG. 69 a shows substantially planarsurface electrodes 333 on either side of a thin film lead 10 thatcontains a single metal routing layer 94, although this single layer maybe composed of more than one kind of metal. In this diagram, theelectrodes are the same size and routed to either surface in analternating fashion, but it should be understood that differentelectrode size and routing schemes could be employed. Similarly,although the electrodes are shown as slightly recessed, it should beunderstood that they may also be flush with the thin film lead surfaceor protruding slightly. FIG. 69B shows substantially planar surfaceelectrodes 333 on either side of a thin film lead 10 that contains twometal routing layers 94, although each metal layer may be composed ofmore than one kind of metal. This arrangement has the advantage ofcreating higher density arrays on either side of the lead. It should benoted that even more metal layers may be used to increase the routingdensity and decrease size of the thin film lead and/or array. FIG. 69Ccshows substantially planar surface electrodes 333 on one side of a thinfilm lead 10 and penetrating electrodes 313 on the other side of a thinfilm lead that contains two metal routing layers 94, although each metallayer may be composed of more than one kind of metal. Note that thesubstantially planar electrodes 333 are actually protruding slightly,which is not a requirement. They could also be flush or slightlyrecessed compared to the thin film lead surface. Also, an array ofpenetrating electrodes could be attached rather than individualelectrodes. FIG. 69D shows substantially planar surface electrodes 333on one side of a thin film lead 10 and penetrating electrodes 313 on theother side of a thin film lead that contains two metal routing layers94, although each metal layer may be composed of more than one kind ofmetal. Note that the substantially planar electrodes 333 differ in sizeand are actually flush. Additionally, the spike electrodes are ofvarying length. The figure shows individually attached spike electrodes.

FIG. 70 illustrates how a flexible array of penetrating electrodes couldbe formed. In this case, a penetrating spike electrode 313, FIG. 70,illustrates how a flexible array of penetrating electrodes could beformed. The advantage of a flexible penetrating electrode array is thatthe exposed electrodes at the end of or on the penetrating electrodesshould end up at similar depths. This overcomes a disadvantage of stiffpenetrating electrode arrays, which when implanted on a highly curvedsurface, such as those encountered in the brain, the active electrodesoften end up in different functional layers of the brain. Thus, not allof the penetrating electrodes are located in the target region oftreatment. In this case (FIG. 68A), a single or multiple penetratingspike electrode(s) 313 is/are inserted through vias in the thin filmlead 10. Preferred embodiments employ penetrating electrodes made fromplatinum, iridium, an alloy of platinum and iridium, activated iridium,tungsten, and titanium nitride. A conductive medium such as conductiveepoxy 381 is used to electrically connect the spike electrodes 313 tothe conductive metal traces 94. The penetrating electrodes could be madeof any conductive and biocompatible medium. When forming suchpenetrating electrode arrays, the epoxy would be cured and then theportion of the electrodes protruding from the back side of the thin filmlead would be covered in a non-conductive medium or layers ofnon-conductive media 360 chosen from biocompatible polymers includingepoxy, silicone, Parylene, and others. Several different penetratingelectrode structures may be employed as required.

FIG. 70A shows two possibilities, a spike electrode and a nailelectrode. The latter has advantages in manufacturing (the electrodewill not accidentally slip through the via) and in maintainingelectrical contact. By covering each electrode individually, theflexibility of the array is maintained.

FIG. 70B, where the thin film lead 10 generally conforms to a surface ofthe brain 11 and so the tips of the penetrating electrodes 313, whichprotrude normal to the local surface of the thin film lead, are notequidistant once implanted in the brain.

FIG. 70C illustrates that the active electrode area on a penetratingelectrode could have different sizes, shapes, and locations along thepenetrating shaft. That is, the penetrating conductive electrodes 313are electrically passivated over some or most of their area 361, and awindow is opened in this passivation at the desired stimulation orrecording site 362. The passivation of the conductive penetratingelectrode may be accomplished through anodization, chemical modificationof the surface, or by applying a coating of non-conductive biocompatiblematerials such as silicone, epoxy, Parylene, and others. The exposedregion or active electrode site may be located at the tip of thepenetrating electrode or somewhere along the shaft and may be made bystandard patterning techniques. The size and shaped of the activeelectrode are also easily varied.

FIG. 71 shows an alternative penetrating flexible circuit electrodearray. The flexible circuit electrode array 700 separates intopenetrating fingers 702 to penetrate different areas of the brain.Further, the penetrating fingers make the flexible circuit electrodearray more flexible to better accommodate the cortical tissue. The brainmoves with minimal forces. The penetrating fingers 702 remain in bettercontact with the brain as it moves.

FIG. 72 shows a hybrid surface and penetrating flexible circuitelectrode array. The hybrid array provides penetrating fingers 702 andsurface fingers 703. As the system is programmable, each electrode maybe used for recording or stimulation.

FIG. 73 shows an insertion tool for a penetrating flexible circuitelectrode array. Since the penetrating fingers 702 are highly flexible,a tool is needed to gently press the penetrating fingers 702 into thecortical tissue. The insertion tool 704 includes spikes 706 designed tomate with the holes of the penetrating fingers 702 and gently press theminto the cortical tissue. The inserter tip penetrates a hole in thearray tip; the very point of the array is bent back to provide ananchoring action to prevent the array from coming out when the insertiontool is retracted, and to prevent micro-motion while implanted.Alternatively, pockets, recesses or other means can be formed in thepenetrating fingers to allow the tool to connect to the array fingersfor insertion.

Referring to FIG. 74, leveraging experience from successfully designingthe chronically implantable Argus™ II Retinal Prosthesis, the RCIimplant will similarly include a coil, thin film electrode array, andimplant electronics housed in a hermetic package. For the RCI, theimplant coil is located subcutaneously under the scalp or possibly onthe brain or dura and will receive power from an external coil placedover the scalp through inductive coupling.

The implant power recovery circuit retrieves DC power from the RF powercarrier to supply the ASIC. Amplitude modulated data from the AES issent to the implant at a data rate of 122 kbps. The transceiver on theASIC chip decodes this telemetry data (referred to as forward telemetry)which carries implant control commands that include electrode selectionfor each neural sensing channel, gain selection, sampling control, andother safety and diagnostic commands. The forward telemetry alsosupports CNS electrode stimulation commands for up to 60 electrodes. TheArgus II implant ASIC is modified to include 16 neural sensing channelsand reliably conveys this information to the AES. The channels eachcontain a differential neural amplifier that senses sub-μV neuralsignals and a band pass filter for a specified y band of 75-105 Hz. Theamplified and band filtered signals from the specified channels aresampled by an ADC without data reduction at a rate up to 480 Hz perchannel and with sub-μV input resolution. Raw data from the ADC isstreamed to the AES directly through a wireless link (referred to asback telemetry) designed with a bandwidth capable of handling the dataflow in real time. The back telemetry data words include a header andCRC to ensure bit error detection. The back telemetry employs aFrequency-shift Keying scheme whose carrier frequency is selected tominimize susceptibility to anticipated interfering signals. The ASICalso includes a dedicated channel and a 1 KHz test signal generator foranalyzing electrode impedance values and thus determining the health ofthe electrode array.

Accordingly, what has been shown is an, improved method of making ahermetic package for implantation in a body. While the invention hasbeen described by means of specific embodiments and applicationsthereof, it is understood that numerous modifications and variationscould be made thereto by those skilled in the art without departing fromthe spirit and scope of the invention. It is therefore to be understoodthat within the scope of the claims, the invention may be practicedotherwise than as specifically described herein.

What we claim is:
 1. A neural interface system comprising: an externalportion including a processor, telemetry circuit, and external coil, theexternal coil sending power to, and sending and receiving data to andfrom, an implanted portion; the implanted portion including an internalcoil receiving power from, and sending and receiving data to a from theexternal coil, a hermetic package, an electronic circuit within thehermetic package receiving power from the internal coil and sending andreceiving data to and from the internal coil, a differential neuralamplifier within the hermetic package, an analog to digital converterconnecting the differential neural amplifier to the electronic circuit,a driver within the hermetic package connected to the electroniccircuit, and a flexible circuit including at least one stimulatingelectrode connected to the driver and at least one sensing electrodeconnected to the differential neural amplifier, the flexible circuitconfigured to interface with neural tissue of the brain.
 2. The neuralinterface system according to claim 1, further comprising a moistureleakage electronic monitor within the hermetic package.
 3. The neuralinterface system according to claim 1, further comprising a band passfilter connected between the differential neural amplifier and theelectronic circuit.
 4. The neural interface system according to claim 3,wherein the band pass filter allows frequencies between 75 and 105hertz.
 5. The neural interface system according to claim 1, wherein thedata includes control commands including at least one command selectedfrom the group of electrode selection for a neural sensing channel, gainselection, sampling control and other safety and diagnostic commands. 6.The neural interface system according to claim 1, wherein the dataincludes stimulation data for a stimulation channel.
 7. The neuralinterface system according to claim 1, wherein the analog to digitalconverter samples at a rate of 480 hertz.
 8. The neural interface systemaccording to claim 1, wherein the data includes electrode impedance.